Wow, that OP is something. First of all, Plat isn't very high ranked at all. I bounce around all over Champ right now, and I know I'm still a world away from Grand Champ, let alone pro levels (which granted I'll never be, but GC is the lifetime goal for my RL). Anyway, at my level, most players are making multiple mechanical mistakes per game. There's not much point in getting mad over that, unless for instance they keep going for ceiling shots and whiffing miserably, or whatever. I try to only get mad at teammates when they are ignoring rotations, refusing to pass to me in open space, or other stupid greedy behavior. But if they're trying to play as a team, even if they fail miserably at the execution, it's all good.
If your teammate says "sorry", say "no problem". If they score say "nice shot", and if you score off their pass, say "great pass", and if they send you a compliment say "thanks". Following those simple rules keeps a solid majority of my games from descending into toxicity. Also, if you're doing well off the start, 2 to 3 goals worth of compliment spam by your team can trigger the opposing team into toxic madness, so win/win.