Explaining the reasons for the fact doesn’t make it no longer a fact. That’s only a spin.
There are other ways to spin it as well:
The Switch, Wii, and DS faced significantly stiffer competition than the SNES. Not only from rival consoles, but from the emergence of smart devices.
The N64 managed higher first party sales on a significantly lower install base. Market sizes wouldn’t even be relevant in this case.
At nearly 200 million, the NES has more than double the first party sales of the SNES. The market was smaller.
It's not spin, its context. If I told you that some 14 year old kid beat one of the NBA's best players at one on one basketball, would you want to draft that kid when he got old enough? Now, what if I told you that the kid only beat him because the NBA player had a full leg cast at the time? It's still a fact that the kid beat him, but context changes everything.
The Wii and DS were not competing with the iPhone. The Wii was a completely different device. As for the DS we can just take a look at the following chart.
Remember iPhone launched in 2007. It doesn't look like it effected DS sales at all.
As far as the N64 selling more first party software, well of course it did. 3rd parties left Nintendo in droves for the PS1, and with less 3rd party games, to compete, sales of Nintendo developed games shot up.
I agree with the NES part. It was Nintendo most commercially successful system hands down.