I agree on PS5, that it doesn't show any signs on how the market should be grown, so chances are with tougher competition from XBox, PC and streaming services that PS5 will decline or at best stay similar in sales to PS4. I agree that PS5 might lose in matured markets, especially Japan they seem to lose any grip on. I agree that developing markets may grow overall, so that PS5 might sell more there. But the big new markets to open up that helped PS grow in the era of PS1 and PS2 are mostly covered by now, so the developing markets also have limited growth capabilities.
But to be fair it was a lot harder to gauge Switch success pre launch. First it was a new concept with the hybrid, and while many - myself included - was entranced by the concept, I lerned to mistrust such anecdotal evidence. How much the market as a whole would like the concept was not so easy to gauge without proper market research. Another variable is Nintendo itself. They have proved time and time again, that they can be their own worst enemy. Decisions like stopping support of the Wii too early, and then follow up with a direction in the complete opposite of the Wii success make it hard to trust Nintendo to do always the right thing.
One thing you could know about Switch was, that Nintendo probably wouldn't fumble support in the launch year. They had a lineup for 2017, that covered a lot of bases. New sequels in established success series (Breath of the Wild, Mario Odyssey), sequel of their hit new IP (Splatoon 2), new IP trying out some stuff like Splatoon did (Arms), port of a proven successful game (Mario Kart 8) and a game showing off the new features of the hardware in the vein of Wii Sports, Nintendoland and Astros Playroom (1-2-Switch). That are six games for the launch year covering different bases. Nintendo didn't needed all to succeed, but this made clear that Switch probably wouldn't end up being a flop like WiiU.
Still, how much BOTW drove early momentum and how well received the hardware would be was hard to get a grip beforehand. Even for Nintendo themself. Soft launch in March allows for course correction before the first holiday, like they did with 3DS. That launch date shows a bit of a lack of confidence.
So yeah, I agree that something big and unexpected must happen for PS5 to significantly outsell PS4. But the success of Switch was much more of a gamble, because Nintendo didn't just do more of the thing before (which would've been a bad idea anyway, as before was WiiU) like Sony does.
Switch's launch year also had Fire Emblem Warriors and Xenoblade Chronicles 2 announced in January 2017, so that makes eight games for ten months. Additional first party software in 2017 (but not announced in January) was Snipperclips, Mario + Rabbids and Pokken Tournament DX, but even before that there was enough on the schedule already. Breath of the Wild had caused waiting lines of ~5 hours at E3 2016, so it was clear that it wasn't going to be on the same level as Skyward Sword, but much bigger.
Switch did not have a soft launch. Its launch was pushed back four months specifically to leave no holes in the release schedule. Six years before it, the 3DS launch was pushed back three to four months due to production issues. So neither the 3DS or Switch were soft launches meant to allow course corrections before their first holiday season; both were supposed to launch during the holiday season, but got delayed for very different reasons.
Switch looking like a gamble is only true when one either willfully ignores facts or is oblivious to them. It was clear for years that NX was going to be a single software ecosystem that would receive all of Nintendo's games and unsurprisingly also bring third party support of handheld consoles to it; the 3DS was plain obvious, and if you are honest, Sony's exit from the handheld market was bound to increase Nintendo's third party support. It was also in plain sight that Nintendo was going to appeal to different gamers than they went for with the Wii U, yes. Then you looked at who they targeted and pondered if they would like Switch, and of course they would when Switch's launch title Breath of the Wild screamed "Classic Nintendo" instead of being more Skyward Sword which is just about as far as you can detach Zelda from its classic appeal. Classic Nintendo always sells, and with Switch Nintendo ticked the boxes for both hardware and software. The only serious question mark was the console price, but if price is the biggest problem of a console, then that's just about the easiest thing that can be corrected.
When we fast-forward a few months to June 2017, the early momentum was good and factual, so which reasons for doubt were there left that Switch wouldn't sell at least 100m units? Just the usual FUD was thrown around, like Nintendo is unable to sustain high sales with their consoles (except with the DS which had strong software support, exactly the same thing Switch was going to have). When you see that a console sells well during its initial post-launch window and know that it will continue to get a lot of quality games, it's safe to say that it will continue to sell well.
Lastly, there are levels to being wrong. It's one thing to be off a little, but with Switch it was so crazy that not even halfway through its life it had already eclipsed more than 90% of people's lifetime sales predictions. Someone who has predicted half of what Switch will actually sell in its lifetime counts already towards the top 10% of predictors despite making a bad prediction. Furthermore, VGC isn't just a random gaming website, it's the place where the people most interested in console sales hang out, where all this stuff keeps being discussed all year long. There's not much room for "I wasn't aware of this or that."
^When a forum makes basic things look like something very special. I still don't think that I had to make any big efforts, but when a community allows me to play on easy mode, then sure, I'll take it. New generations occur only every several years, so such opportunities where the vast majority puts blindfolds on don't come around often.
One last word of clarification, my point is not "you dumb mnementh," but rather "be smarter than that, don't keep making excuses for it, acknowledge that it happened and learn from it." I've been here for a long time and the people who excuse bad predictions are the ones who are pronest to make bad predictions themselves. While it is enjoyable for me to see old threads and people who got owned, it's frustrating that so few people seem to properly understand the console market. I don't expect PS fans to understand Nintendo, but when Nintendo fans repeat pony lines time and time again... well... I don't know why these supposed "truths" don't get challenged more often. You'd think that Nintendo fans would be interested in learning more about why Nintendo is the best to ever be in this business, but apparently not.