It hasn't been issue on the Switch thus far. Nearly every Nintendo franchise across the board has had its best selling game on the system because not only has the studio had the proper marketing, support, and resources behind it to do it. It has had the foundation successfully put in place where that game is automatically starting from a position of strength, rather than weakness. Right out of the gate, it is in a position to where it can achieve those numbers and Metroid should be no different. Fire Emblem, Pikmin, and Xenoblade aren't exactly A-list franchises either. But all three of them are not only succeeding on the Switch, they're thriving. That's what happens when you have a system that is white hot like the Switch is, everything sells. Because the casuals who love the brand will automatically associate the game with the brand and THAT'S where those other buyers come from. So, if Metroid DOESN'T sell, while everything else is... That is not a good look. At all.
Yes, all those franchises experienced some increase in sales, but to say they are "thriving" in my opinion is quite a stretch, they did better than in the previous entries and that's it.
Also, I don't think any software is guaranteed to sell well until people get to actually see the game.
Pokemon is arguably the second biggest Nintendo IP and even being released on Switch it won't be the best selling Pokemon, because the game is trash. Not even the massive amount of money Pokemon Co spend with marketing (probably much more than the game budget itself) was enough to change that
Edit:Also NSMB U, not even adding Wii U sales will be the best selling 2D Mario, so here you have it, the sales of any software will depends of the software itself and not only its platform
Let's just calm down and wait. Even if Dread don't outsell the previous entries doesn't really mean the franchise is doomed as you imply
You examples don't make any sense.
Pokemon S/S is selling huge numbers. Yeah it's not going to beat the original Pokemon, but no Pokemon has come close to that, and S/S will obviously be the second best selling Pokemon game ever. So if you think it is a terrible game that pretty much proves your whole argument wrong. Of course it isn't a terrible game, but anyway this example doesn't make sense.
And NSMBU....ummm there are numerous 2D Mario games that NSMBU:D won't even come close to, so I have no idea what you're talking about there. But considering it was a low marketed port that Nintendo just threw out there in January and isn't particularly great for a 2D Mario game its sales have been phenomenal.
Basically, Nintendo IP have monster sales on Switch.
The problem with Metroid Dread is its a $60 game. At $40 (which is about what feels right for a first party 2D side scroller not called Mario), I think it could sell around 3+ million which would obviously be great for a Metroid game. At $60 I definitely see this being limited to 1.5 million, and the only reason it'll get that high is because it's on the Switch. I certainly won't be buying it at $60 even though I'd love to play the game, and I'm guessing by the time it is on sale for say like $30 I'll already have MP4 and won't even be bothered about getting Dread. This is gonna be like Link's Awakening remake. Great game that lots of people are excited about but launching at $20-$30 higher than what makes sense so sales are going to quickly die after the first couple weeks on the market.
Franchise is of course not doomed no matter what happens, but sales will be low because of pricing. If they priced it right, combined with the pent up demand for Metroid, plus Switch's install base, I think it'd sell really well. MP4 will be the true test of Metroid's popularity. With the critical popularity of the Prime series, the years long wait for it, and Switch's well over 100 million user base by the time it comes out, MP4 will hopefully go after 10 million in sales thanks to the Switch boost.