I'm basing my opinion on 1 significant new game in three months not constituting a constant flow.

1 major new game in the first three months just doesn't feel like enough software was ready, that's all. 

Actually no, history has not shown me incorrect. No amount of sales can change that one significant new release in 3 months is not a "constant flow". There is nothing you can say that will change my mind.

Skipping 1 month without a new game would be fine, but they also skipped April as MK8 was an old game.

It wasn't an issue for me personally as I simply didn't buy a Switch until it got more games. Games being new is important to me though so I just can't help but get the feeling from Switch's first few months that it was too light on new software. That's just me.

Nintendo faced a serious problem with both the Wii U and to a lesser extent the 3DS when they came out in that development times skyrocketed. One major problem they faced was that for much of Nintendo's first and second party developers it was the first time they had ever worked in HD game development and standards were higher in 2012 than they had been in 2005-2006 when the 360 and PS3 launched. They couldn't wet their feet with games of the graphical quality of early pre-Gears of War 360 games like other developers had. This ramped up development times, and games that could have sold the system like Mario Kart and 3d World couldn't come out in time partially as a result. I wonder if that's the reason NSMBU came out when it did so close to the 3DS version and seemed so half-assed. It was a good game, but everyone knew it could have been much more if the proper time and effort had been put into it, especially on the visuals. It was something Nintendo could get away with not making a graphical tour de force at the time. Games like Mario Kart 8, DK Tropical Freeze, 3D World, Smash 4, Yoshi's Wooly World and Kirby Rainbow Curse needed a lot of time and care to look as good as they did and still be playable.

The 3DS had a similar problem. It may not have been HD, but with its circle pad, glasses-free 3D, and near-PS2 level graphics Nintendo wasn't making as many 2D games for it like they did for the DS and those 2D games take a shorter time to make. The 3DS eventually benefited from not being in HD and having much better third party support so that it had a steady stream of games from late 2011 through 2016, but it could have used some more 2D love that first year to fill out the release schedule.

The Switch benefits from Nintendo now having years of experience with HD games development, being able to upres Wii U games to fill out the release schedule since no one had a Wii U, having nearly all of Nintendo's focus since the 3DS has not had that much support since 2017, and having pretty good third party support.

On an unrelated note, the GBA-DS situation is different from all the others. Nintendo continued to support the GBA because they thought there was a good chance the DS would fail and so the GBA would be their backup handheld with the built-in install base. That's part of why they didn't make the DS an official successor to the Gameboy line and called it a 'third pillar.' If Nintendo knew just how successful the DS would turn out to be then I think they might have called it the 'Gameboy DS,' or something like that to preserve the Gameboy brand.

I hope Switch 2 is not rushed to market. Anything before Holiday 2022 would be rushed, and some would argue that anything before Holiday 2023 or March 2024 is rushed.
Switch 2 has the potential to be Nintendo's greatest platform of all-time. We're mid-way into the Switch's life and we still have not seen most of the benefits of Nintendo now having a merged home console and handheld library. Switch 2 should be able to fully capitalize on that. Switch 2 really needs a strong first-party launch title that is exclusive to it. Breath of the Wild has done amazing on Switch, but it was released at the same time on Wii U. And it was a game that had been announced about 4 years prior to its release. Launching the Switch 2 with Mario Kart 9 (if we don't get it on Switch), would be a fantastic idea. Or maybe we'll get Mario Kart 9 on Switch in 2021/2022 and then Switch 2 has a deluxe version of it at launch or in the launch window.

OP gets these right
Atari 5200
Atari Jaguar
Sega Saturn
Nintendo DS
Nintendo 3DS
Nintendo Wii U

OP gets these wrong
Nintendo Game Boy Advance
Nintendo had been waiting for a long time to release this system.  It wasn't ready yet when the Gameboy Color was released (and potentially too powerful), so the Gameboy Color was released as a stopgap.

Xbox 360
This was really the system that Microsoft had been planning to release from the beginning.  The XBox was the trial run and the 360 was the real thing.  The RROD was more a result of inexperience with hardware than it was because of excessive rushing.

Nintendo Switch
This system has one of the best 12 months of first party releases for any Nintendo system.  It might even be argued it has had the best first 12 months of any system.  Nintendo planned the launch year out very carefully.  No way was this a rush job.

OP leaves these out
SNES
The Super Famicom was definitely a successful system, but it was also rushed, at least in Japan.  NEC and Sega had already released their next gen systems and Nintendo had to play catch up to get out their 16bit system.  Super Mario World definitely felt rushed even though it was still a good game.  I mean in Mario 3 the big new powerup is a Racoon Tail where you fly, while in Super Mario World the big new power up was...a cape...where you fly.  Wait isn't that the same thing?  Yeah, definitely a rush job.

Gameboy Color 
Nintedo's plan for a successor to the Gameboy was the Virtual Boy.  The VB flopped.  Nintendo was vulnerable and it was too soon for the GBA.  The Gameboy Color was a rushed stopgap until the GBA was ready.

XBox
This was released late and canceled early.  Basically a trial run for the 360.  They just needed to rush something out there to get some experience, before they were ready to pull out the big guns for the 360.

The problem with Saturn was it was built with 2D in mind but when they got wind of the PS1 and it's 3D polygon approach.they changed the Saturn to dual processors and that lead to as you put it a complex mess , they should have delayed it and added a singe 3D capable processor.

yes, it was expensive but ambitous,  but it was future proof as well, look at xbox 360 inital version, no hdmi (just component video), no wifi (needed adaptor), dvd rom based (hd dvd add was a failure, but nothing to do with ms, however, high capicity hd dvd would be useful in games), compare to ps3 at start, bluray, wifi, standard 2.5" hdd, hdmi, very future proof, esp in recent years as newer tv sometimes don't have component video,