Paper Mario used to be the definition of niche.
To put this in perspective: Paper Mario and the Thousand Year door released on a cube with very little JRPGs. It sold alright. About 2 million units. That was very low in the console generation absolutely dominated by JRPGs. Randomly throw a dart at any high profile PS2 game, and I guarantee that that PS2 game would sell leagues better.
Kirby games are historically not great sellers too. Besides the original, the best selling game pre switch was Squeak Squad with 2.27 million units. They always reliably sold of course, which is why they were still made, but Kirby was hardly a sales juggernaught, HAL could just make a lot of games pretty cheaply
On the PS2, Final Fantasy X sold a massive 8 million and it was a huge series in the industry. One of the best selling of the time. Final Fantasy 7 also did 10 million and it took Nintendo's marketshare.
But now look at how everything has flipped.
Kirby is now sitting pretty at close to 8 million units while Final Fantasy is struggling to pass 3 million. Paper Mario, even a divisive game like Oragami King, seems to be easily outselling FF7 rebirth. These were games that had 1/4 of the sales previously, but now they have completely flipped. Nintendo properties are stronger than ever, Nintendo is hiring a whole army of developers now(and a brand new building), while Square is doing layoffs.
Now the whole situation is reversed. Nintendo used to really need Square, but now, it's square that desperately needs Nintendo.