Again, these are just opinions, but pro-coaching from the stance of "it's not going to change anything," is sort of pointless. Coaching will, the overwhelming majority of the time, only impact close matches anyway.
I already said that coaching makes a difference. I just think that A) the difference it would make is tiny relative to how badly people on this thread are overreacting to it, and B) the difference it would make WOULD be more toward player vs. player.
Why is player + coach vs. player + coach any worse that player vs. player + crowd? Or player vs. player + jetlag? Or player vs. player + (insert stressful circumstance)? No reason, other than the fact that we are used to those sorts of situations. What we have right now is a system that compares your "average day" with your opponent's "average day" with a slight advantage to those who live near or have friends/family near the tournament (more likely to be having a better day). With coaches, we would have a system that compares your "best day" with your opponent's "best day" with a slight advantage to those who put in the effort to seek out a good coach and practiced a ton to work well with their coaches in game. "Working well with a coach" skill because
I feel like I'm the only one who sees that having a coach can be a double-edged sword. Teaming up with a coach can increase your net knowledge capita but decrease your knowledge exchange rate. Coaches are not big, ominous bags of unfailing wisdom, the answer keys to all things Smash. They are human beings, they can be read like human beings, they can crack under pressure like human beings, they can make mistakes like human beings, they can get into fights with their players like human beings, and they can be exploited like human beings.
If I were up against the sort of coach who would say something like, "Hey, he likes to tech in place, you should punish him for that," I would purposely provoke him into saying it by teching in place twice (thrice, if I'm feeling lucky) in a row. If I fool both, I get a free read. If I fool one, I've forced them to have some sort of communication (which will take the player's mind away from the game) and I might still get a free read on top of that. If I don't fool either, then I will be punished no more horribly than if my opponent were by himself.
Not phrasing things too well right now on account of lack of sleep, but I have a pretty clear argument in my head. For now, tho, I'll just stick with calling it "survival" instead of "singles." I hear it's more socially acceptable to "survive" with somebody's indirect help than to be "single" with somebody's indirect help.