Yes, according to history Nintendo did depend on third parties, but they ruled them with an unwavering attitude. They couldn't spread to Sega because Sega during the Genesis era couldn't spread their marketshare until the SNES era and had to rely solely on first party which made everything from action games to first party sports titles just to measure up. Eventually when the Playstation and Saturn came there was alternative hardware with CD technology and Nintendo was afraid of piracy so they stuck with discs. Third party wanted Discs, especially since the trend with CD roms was already the norm on PC in the mid 90's. Nintendo stuck with cartidges and sealed their fate and lost half of their marketshare because of it.
Pachter has not been wrong about all things Nintendo, and obviously the man is not perfect, but he has to have done something right as a Wedbush analyst or else he wouldn't have a job.
I'll bet the Wii U without third parties will struggle to reach forty million. The reason I say this is because without third party the first parties audience doesn't grow exponentially, it generally stays the same. The Wii's case was widely exceptional.
If you have paid attention to the sales of hardware, all consoles that lacked third party have had a hard time winning any generation.
A) The Wii had a lot of third party support. A lot. It just didn't get the lion's share of major multiplat titles the other HD consoles were getting.
B) Pachter is a joke, as is referencing or citing him in any video game discussion. Just because the man is a legit business analyst, does not mean that he actually knows the first, second, third or even fourth thing about video games, the video games industry, the history of said industry, or gamers themselves. Because with most things he says he clearly doesn't, and he contradicts himself (aka goes back on shit he previously predicted) all the time. The dude is a joke, and the only reason any of us know him is because for some unknown reason GameTrailes whores him out. Had it not been for GT, none of us would even know his name.
C) Wii U didn't lack for third party support at launch, in fact it was quite strong then. It has dried up since because of the sales slump of the system, which ironically was caused by the software drought. Certain third party companies seem to expect Nintendo to sell their hardware with their own games (Which they do, if only those games had come out sooner), but they don't realize that, as you yourself stated, third party expands the potential audience/customer base of a given console. Third party devs providing stronger support for a system could be considered a business investment in making the potential customer base of that console stronger in the end, which would result in greater net sales for their own games over time. But some companies, specifically EA, don't seem to see it that way, which is their own short-sightedness coming to bear, and no idictment on the system itself. The sales of the console WILL pick up, and when they do, there is no legitimate excuse on earth for most third party devs to not at least provide cheaper-than-they-let-on-to-make multi-console ports for the system, at the very least.