I'm kind of on the fence about this, PRO is very unique, having a gen 6 metagame with a gen 4 mechanic of not having team preview. It's one of the only places where you will find something like this and personally I love having no team preview, yeah its definitely more stressful but it can also be much more balanced. With team preview there can be some games where the match is literally decided before it even starts. For example, lets say my team gets annihilated by Garchomp. My opponent could capitalize on that and keep their Garchomp hidden until it has the ability to start setting up, but at the same time he might not know that my team loses to Garchomp, and decides to send it in and get up his Stealth Rocks and maybe even lets me weaken it. Now at this point, I know that I need to be careful what I have on the field so the Garchomp can't come in for free. As the match goes on, it basically becomes a gen 6 battle with "team preview" because more and more team members get revealed. In a battle with team preview, my opponent could recognize this before even making a single move and shift their playstyle to be more careful and observing so they can pick the right moment to send it in and end the game. The entire game could be 5 of their Pokemon supporting their Garchomp sweep, where as only 1 of my Pokemon would be able to deal with it unboosted, meaning it would have to be sent in at the same time. Essentially the opponent would have X amount of turns to send in Garchomp and end the game while I only have 1 turn to predict that switch-in, or else I lose. (Of course you could just make sure your team has checks for common Pokemon like that, but it was just an example, and no team can check everything.) Obviously all of this could just be voided by writing your opponents team down for the next time you fight them, but I feel it would still remove a layer of strategy from PRO.