Babylon 5 is an early 90s Sci-Fi show that was ahead of its time in concept. Then most Sci-Fi was more about fantasy and episodic so each episode stood on its own. Babylon 5 took a darker more grounded approach to Sci-Fi and it did what all shows do now. Every episode bleeds into the next one. So it has a story arc so each season is a chapter. It's not as smooth as a modern show like a GoT early seasons but for the time it was novel and pretty well done despite not having a huge budget(they could not afford models so they used linked Amiga 2000 PCS to make the ships and station out of CGI and it aged badly). Some believe and debate that Star Trek DS9 ripped off Babylon 5 as there are many surface-level comparisons and some history with the Fox Network. My understanding is that is still a fan rivalry between the two series.  It's worth watching on Tubi TV for free.  Like these kinds of long story show, it starts as a slow burn.

In a Nutshell, it was basically Paramount with Warner Brothers, then Paramount against Warner Brothers. The whole Babylon 5 story arc was initially presented to Paramount for their planned PTEN Nextwork. So they knew it when they went DS9. From there on, "theft theories" were plentiful, but this might have been a smoking gun:

A commenter named Steven Hopstaken left the following comment in the io9 article:

I was working at Warner Bros. in the publicity department when Warner Bros. and Paramount were preparing to launch a joint [emphasis mine] network. Warner Bros. already decided to buy Babylon 5 for their adhoc PTEN network (a group of independent stations that agreed to show Warner Bros. shows in prime time.)

Paramount and Warner Bros. both agreed that Deepspace 9 would be the show that would launch the new network and there wouldn’t be room for two “space” shows on the network. I was told they purposely took what they liked from the B5 script and put it in the DS9 script. In fact, there was talk of leaving the B5 script in tact and just setting it the Star Trek universe. I had to keep rewriting press release drafts while they were trying to make the final decision.

But then, suddenly, Paramount decided to launch a new network on their own and screwed Warner Bros. over. That sent Warner Bros. scrambling to create their own network; grabbing up any station not already committed to Paramount and getting WGN to show the WB network on cable.

So Paramount definitely knew about the Babylon 5 script, I don’t know about the DS9 show runners, but I find it hard to believe they didn’t know.

At the time, I thought that when DS9 went fully into the Dominion war arc (no more "alien of the week" episodes), DS9 was pretty much a ripoff of B5, idea-wise.

I’m actually surprised so many people didn’t see Babylon 5 until recently as I didn’t know anyone new watched it after the 90s :D

It’s that the show is from the 1990s, but looks like the filming took place in the mid-80s, despite the wicked CG.
If anything, Babylon 5 is probably the most well planned show in science fiction history. I’m a big fan of the episodic seeding into the more novelized approach from late season 1 to the end of season 4. IMO, the finale of season 4 is the last episode that should be watched (as in, watch it after season 5), as it spoils a lot of season 5, and is also a very good ending to the series. Season 5 has the weakest stretch of the show as it doesn’t really leave the runway until the season’s about 65-70% over, which is completely unlike the prior 3 seasons. Season 1 works because it’s a light-entrance into the universe of Babylon 5.

On the influence of the revolutionary formula of Babylon 5:
Stargate SG-1 and Farscape both used similar formulas, where the shows began episodic and transitioned into TV-novel form. Battlestar Galactica was the first that was just novel form right off the bat, at the time that was a rare thing outside of WWF RAW and soap operas. Deep Space 9 and Voyager were more arcy, but we’re still largely episodic, usually only having the arcs as a backdrop, dropping them into the main focus for an episode or two every now and then—sort of like Friends and Season 4 and 7 of Seinfeld. Caprica was even more of a novel than Battlestar Galactica. And for a while I thought Babylon 5 was the ideal format, use season 1 as a hook and then get into the story during season 2 and on… until Ronald D Moore (BSG/Caprica) did For All Mankind, which I think is probably my favourite show format to date—it’s like every episode is a chapter that feels distinct, and yet integral to the story as a whole. His former Star Trek writer colleague, Bryan Fuller, did a similar thing with Hannibal, HBO kind of did it with Rome—although at least half the episodes of Rome still run together in the way TV-novels tend to (Game of Thrones usually had 1-2 distinct episodes per season, usually the second last one is one).

I fucking love a certain episode of Babylon 5… I won’t spoil it only say it involves Delenn and has the line, “They are behind me, you are in front of me” - I normally hate blatant plot mechanics, but this “all is lost” mechanic landed fantastically.

I recommend Babylon 5 to any science fiction fan who can get over the visuals and often wooden acting. Even if you didn’t like TNG era Trek… Perhaps especially if you didn’t like Star Trek’s TNG era Star Trek: Babylon 5 seems to be the #1 show among scifi fans who didn’t like the TNG era. Although, I don’t know about younger fans who grew up after the 90s.

Shows still had plenty of differences and it's obvious showrunners got over it. They had actors crossover for a couple of episodes from each show. And boy even Majel aside did I notice the 1 million Star Trek actors on Bab5. Obviously Chekov but G'Kar was Commander Tomalak on TNG. Many more but yeah. 1990s was rich with Sci Fi TV.

The setup for the series in season 1, with a fallen nation (the Cardassians) that eventually become the beachhead for a powerful outside alien force is directly ripped off of Babylon 5. The Cardassians follow the same arc as the Centauri. The difference is Babylon 5 is larger in scope and far more cohesion. Babylon 5 had more factions, more dimensions, more intrigue, and wasn’t so blatantly anti-military as DS9–which basically made military people look like a bunch of buffoons and you’re English School Teacher Benjamin Sisko substantially more skilled than all of them.

To be fair on copying, Babylon 5 is hardly without sin, JMS did take a lot from Tolkien (especially the Silmarillion) - The Vorlons, for example, follow the same arc as the Valar/Valinor mixed with a Cold War style hesitancy to engage directly with the enemy (Tolkien doesn’t really explain why they hesitate until they’re asked by Earendil before the War of Wrath). But JMS also directly acknowledges the Tolkien parallels with homages.

The funny thing is Star Trek TNG is my fave show of all time by far. I grew up with it. I've taken life lessons from Picard's character. I was never a big fan of DS9 and I disliked it when it went to war. Voyagers writing so so hit and miss and a lot of miss but I rather watch Voyager as it still tries to be Trek and has some fun episodes. I did find B5 more cohesive than DS9. DS9 had a big budget and on the flip side, for a 5-mile-long station it sure felt cramped a lot, DS9 felt bigger despite being a fraction of the size of each faction. B5 did a lot tho with a 3rd of the budget DS9 had. So I don't hold some of the cramped sets against them. If the live-action reboot happens, I don't know if any details have come out but I'd hope it's a start over. I'd like to see them even with a modest TV budget now CGI and sets plus green screen can be a massive upgrade over before.

I liked B5 for what it was, SciFi with some great characters and ideas, on the limited budget. As a Trek fan, I didn't like DS9 at all, but B5 more than replaced it for me.
Still think Farscape is best of the SciFi with some great characters and ideas, on limited budget, made for geeks. I miss those kind of shows, apart from Killjoys and Dark Matter there hasn't been much in that vein (not that either of them really compare to earlier shows) fro quite some time.