How would battles become unfair because of a change in number? By that logic, battles can already be unfair with just 6 pokemon in a team.
Strategy would not be reduced. It may change depending on the number, but strategy would keep a ratio with how many pokemon players are allowed to use. You think it would make things easier on you, but you don't see how it could be harder when opponents take advantage of the numbering as well. It doesn't become so easy anymore.
Insanely long battles can depend on the number. 8 pokemon teams wouldn't be much worse, the most acceptable for me probably being 10. But this is why options can be put in the battling systems. Don't want to battle with 10 pokemon? Choose an option to battle with 4. Or 6. Or 2. With that, everyone wins as the only change is a couple more features. Even if HYPOTHETICALLY (as in I don't see thios happening) we can use 100 pokemon, who knows if some people wouldn't enjoy that? I wouldn't, but I'm not the only person in the world. Other people may enjoy different things.
Let's see, increasing the number lets players use too many Pokemon which'd otherwise be restricted. The offensive component of a team could now consist of Lucario, Gyarados, Infernape, Scizor, Dragonite and Heatran whereas normally, that'd be restricted. I don't want to up against something like that. 6 Pokemon
evidently doesn't make battles unfair, because people would've noticed if it did. 6 wasn't just an arbitrarily chosen number; I'm sure Game Freak tested the game to find out how many Pokemon would be optimum. And it's worked out well.
Building a team requires less strategy and thinking when you can throw together a larger number of Pokemon to do the same job that 6 needed to do previously. During the battle, you have access to say, a larger number of sweepers or a larger number of walls to safely switch in and stall your opponent to oblivion. And no, this doesn't cancel each other out because opposing teams aren't necessarily polar opposites of each other.
We already have options, 6 or below. The problem with making a higher number the "standard" is that the standard format would be broken and that's never good. There's also no way of restricting it in-game.
And just because someone wants 100-Pokemon per battle doesn't mean that it should be implemented, nor does it mean that it's a good idea.
Because Nintendo is Satanic, and wanted to piss off the Catholic Church by using 6, the devils number
Thought it was 5 or 666.