Care to explain your point about "MORE RESTRICTIONS = FEWER REWARDS"? Because ban SoGs wont make them unavaliable in the bonus spin, if you dont know. It will make them unavaliable in normal spins, where the chance of a person that dont have them (possibly a newbie) get them, considering the win rate, should be like 0,1%, if not lower. And yeah, just a newbie would try get upped shards directly from Gold / Platinum instead of getting them in Bronze league. Ban SoGs wouldnt do any bad to people without shards, as you claim.
To me, there is a super valid reason to restrict how people make decks: diversity, and then a more enjoyable and interesting experience to all.
New people would probably be the ones that care less about ban QT and Shards, they usually dont use them. Rainbows usually require a lot of upgraded cards. Anyway, if a person is lv 10-19 and is in a competition vs people of same level, and under same rules, its fair even being harder. Make a good deck and win. Why everyone needs an easy option to use a rainbow deck? Doesnt it beat the purpose of using the oracle card in the deck?
According to you: annoying monos/duos = bad; annoying rainbows = good. The reason? You are a "pro rainbow slayer", huh? Oh, great, you beat them all. Other people dont. If there is a diversity of hard decks (looks like its the idea that scares you), then you will win less, and other people will win more. You can create a deck that can have some good match ups and some bad match ups, as everyone. Balanced, enjoyable, just... perfect. And I bet we will see good decks you havent even imagined.
To me, its not just a matter of losing to rainbows, its a matter about playing the same boring game, and again, and again, and again, with a eventual interesting fight. If you care just about winning, I have a suggestion: you can play AI2. These you will "have a good chance of beating", too.