Re: why do you keep mixing ranks?
I'm having the exact same issue. Only recently started playing ranked and blitzed to plat, only to start consistently being put in lobbies with preds where I'm way out my depth. Just finished a match where I was killed by a full predator squad including the #3. Why am I playing the #3? It takes the fun out of it, it would be much better to wait double the time for a game but only play against other plat players.
Another issue with the ranking/matchmaking is the fact that you cant get deranked. There are so many plat IVs who consistently go hot drops alone and die without caring because they're stuck at 4800, so they dont care, and it wastes the match for their teammates. With such a big jump between gold and plat especially, you HAVE to be able to derank.