I start with the last because it is not true that in custom games the level of the players against the beginners is higher. There is everything (always more deviating towards the bottom than towards the top) and you do not play ranked, in ranked you play against people of a similar level as long as you find a quick game and easy and effective strategies have always existed in RTS.
I guess you have never played a game like SC2, number 1 a few years ago and with a lot of traffic, the competitiveness of that game did frustrate many players (the games could end in 3 minutes) and still it had and has a lot of traffic, balancing in favor of High level.
Nobody forces the players to play against the players in multiplayer (being able to play and practice against the AI) or to play in ranked, having more game modes. If you cannot counter a strategy, you find a way to do it and stop crying or leave the game, since it is not made for you.
What you cannot do is balance to the liking of the low or average levels because they do not have enough knowledge (the vast majority) of the metagame.