Because it's on track to pass or come close to Wii Us lifetime sales in its first year alone and still hasn't had a holiday season, most of its system sellers, hardware revisions, etc.

i meant what was his justification for thinking it wont even do Wii U numbers

Well really Nintendo is marketing it as the successor to the Wii U, so by that logic it is already a success.

And now, the realization that the Wii U has failed to match the sales of any mainline Pokémon game. Damn.

I don't really see a problem with that argument as long as the conclusions people take from it are consistent with the argument at larger. The Vita was marketed as a successor to the PSP, and is considered a failure. The PS4 was marketed as the successor to the PS3, and is considered a success. The Switch is currently marketed as the merging of Nintendo's markets, so people comparing it to a comparable 8th gen merging makes sense. It's ultimately fairly pointless (as with the majority of such comparisons), but the argument has no inherent logic breaks as long as it's presented wholly. At its core it's not much different than when people compare the overall sales of a brand in any given time period.

It's not even so much about Nintendo treating it as a home console, it's just about how they're still trying to pretend the 3DS is relevant alongside the Switch (though yes, it seems like that won't be the case anymore in a near future... or at least we hope so).

Best realization ever. Never thought of that..

As rocket raccoon already pointed out, last time I checked, Nintendo still refers to Switch as a home console. With that said, I do see your point about if it were to be marketed as a successor to both it would be more fair. The comparisons don't bother me anyway, I guess I was just wondering the reasoning of it. Thanks for giving your opinion on it

No problem :) I should note though (expanding on what i said to mZuzek at the end of my last comment) that even if i think it's an acceptably coherent argument, it is also fairly pointless no matter how it's handled (at least in a vacuum). The 8th gen has been an overall install-base decline for Sony, yet i expect we'd agree the former has been a much brighter period for PlayStation. Likewise, it seems reasonable to predict that the Switch will mark a similar rise in prosperity for Nintendo regardless to whether it sells more or less than the 3DS + WiiU.

Because Nintendo handhelds have always sold about 70 million, minimum. (The 3DS will get there eventually, in fact, it'll do it before the year is over and could end up at 75 million.)
The Switch is the 3DS' successor, as well as the Wii U's. Thus, it's getting every single bit of 1st party support that would previously be divided across 2 systems.
Thus, going from a combined figure of 75 million (3DS) or 88-90 million (3DS + Wii U) to just 45-50 million, despite getting all the signature Nintendo 1st party support (Mario, Pokemon, Zelda, Animal Crossing, Splatoon, Fire Emblem, Metroid, etc.) + decent to great 3rd party support would be a colossal disappointment and failure. That would be Xbox One levels, which the Switch is absolutely demolishing at the moment, launches aligned.