As others have mentioned, most big AAA games do not come to Switch. I think the average gamer wants to play most of those games, and doesn't want to stay a generation behind (because that's what the vast majority of AAA, third-party games on Switch are). And, if I'm correct about the average gamer wanting this, and since we're talking in general, that would make the Switch not viable as an only console. It certainly could be a primary though, as having a PS or XB on the side would allow access to pretty much all of these current AAA games.
But, I take issue with the premise in the OP. There is no way to really boil gaming down to generalities like this. One's tastes are completely subjective, and one's needs are very personal. I like shooters, I don't travel a lot or commute by public transit, and I want access to the big games of the day. So, Switch doesn't make sense as a primary or only console for me. If you prefer other games, sit on a train for 60 minutes per day and spend a half of your life traveling for work, Switch could be the only system that makes sense for you.
We can also look at this without considering Nintendo. I own every major system on the market right now. I think PlayStation has the best first party lineup, and I want to play those games. But, the single most important franchise to me in all of gaming hid Halo. So, if I had to choose an only console, it would be Xbox. On the other hand, my primary console is a PlayStation 4, because that's where the games are. So, as you can see, the topic is very complex, and extremely personal.
You don't have to sit on a train for 60 minutes or spend half your life traveling that's a misconception on enjoying the Switch as a console, why the NS works well even as a primary console is that as a platform it fits multiple gaming habits while having a strong library regardless of taste.
In regards to AAA titles that is actually one of the most back and fourth arguments people are bringing up because AAA is not indicative of quality or being must have as a number of AAA games in recent years have fallen short with F76 being a recent example and other examples include the likes of Destiny and its sequel.