#1, Teaching: they're aware of this, not a lot of MOBAs have tutorials this early on, but they're working on it, in the mean time you can try looking for players to help you learn. personally I don't think items are too complicated, a little overwhelming at first but once you know what the different stats do it all falls into place.
#2, Matchmaking: what do you want, shorter queues or better matchmaking, because at this point in time you can't have both, the community just isn't big enough. also it doesn't just use level, it uses a hidden MMR, your level does factor in to an extent but it's far from the only source. but yeah, you need to understand that while there may be more then 100 players online how many of them are already in matches or not queued, and of the remainder how many are appropriately ranked/grouped to be matched with you? considering we still get pretty large sways in skill level I'd say not a whole lot.
#3, Exclusivity: two unique skins and one pallet swap is hardly a problem, if they show a trend of making exclusives I'd be dissapointed but so far they're doing pretty well.
#4,Causticity: maybe just try being nice? this is just one of those things that nothing can be done about, some people are dicks, double so when they feel they've been dealt a losing hand, best thing you can do is to not be part of the problem, if someone is performing badly then maybe try to help them out rather then picking a fight.
#5, Expensive: I don't think so, I find I have anywhere from 5-10 thousand merit sitting in my bank at any given time and I don't even play that much, as long as you set yourself clear goals it doesn't take that long to buy the things you want, and even then you don't need most of them.