I still don't see the point of OP's complaining. You can't decide what other people are going to play. They are going to play whatever works and what they can afford to build. Not everyone has 6 upgraded cards of everything.
And strategywise you must realize that even if you're against rush decks - for instance - your deck has to have some capability to counter those rushes, otherwise it just fails and drop off soon. Same thing with denial decks, you have to have something to counter them and so on. All of this comes down to having the most effective and balanced deck combination, which currently happens to be a rainbow deck. All mono decks have some kind of weakness(es). Discord and earthquakes for two.
This isn't saying that rainbow decks wouldn't have weaknesses. They have, but the players aren't playing decks that would specifically counter rainbow deck. A deck that sacrifices a lot to counter rainbow is likely going to fall apart vs. fire rush, which is another common deck seen in arenas. So this is how it is: build the most effective deck and don't listen to scrubs saying card / deck x is imbalanced.