It's shorter than 6vs6, yes, but 6vs6 can often go from 30 min to even 60 min per battle...
Switching less actually makes MORE pokemon viable, not less, because entry hazards are much less common. "Less potential pokemon to look out for"? I guess if you mean the exact opposite, then yes. You still have to look out for your opponent's entire 6-mon team, because you don't know which 3 they'll pick. And, again, more pokemon are viable in 3vs3, not less.
For instance, people who only know the old, Smogon way of doing things think you must be crazy if you think Mega Blaziken or Aegislash is a fair pick for standard, non-uber battles... but while both are still powerful, they are forced into checkmate easily, and are actually not overwhelming.; they can coexist in harmony with pokemon like Pyroar or Vivillion.
Part of why this is so, besides fewer entry hazards, is due to hold item variety. Items like Focus Sash and Choice Scarf rule the meta, while set-up sweepers are all but useless in most situations. Things like Choice Band and Leftovers are still important, but Eject Button, Rocky Helmet, and Red Card are also extremely valuable.
Back to that Focus Sash and Choice Scarf comment. Focus Sash will almost always be intact, so it allows you to use it defensively (design a perfect counter), or offensively (design the perfect sweeper). Meanwhile, it is soundly beaten and checked by any kind of passive damage, second attack, or multi-hit. It's powerful, but not broken. The same goes for Choice Scarf: Scarf cleaners become extremely potent, but the limited opportunities to switch Pokemon turn them more into pawns in a larger game of chess. Also, since you can't switch much, it's common to get locked into the wrong move... suddenly, your unbeatable trump card gets outplayed by an intelligently selected type resistance surprise.
The meta is fast-paced, an adrenaline rush, with multiple layers of strategy. To say 3vs3 is simpler than 6vs6 is just delusion. In the end, it depends on how you look at it, but at worst you can say it is equally complex. All the basic tenants are present; it's still a game of Pokemon. However, you have the "see 6, pick 3" layer, and all that entails for team building. You are exchanging the frequency of one strategy for another, given, but the format is extremely forgiving in what pokemon can viably coexist, compared to concepts like OU 6vs6.