Dude... fix your game. your update has no sense of balance. colosseum is a joke, grindy as f for trash rewards, opponents level are all over the places - i just got a player with 22.2k hp and a full light perks deck as a L5 opponent. We all know mofos with that type of build ain't L5. That was my first time seeing that kind of stats in L5 opponents and I'm sure it wont be the last.
As person who fits this criteria (L5 rated with 30.2k HP, full green perks, base damage of 1093), I'll explain why I haven't progressed further up the ratings to L2 or L3, where I probably should be.
The simple answer is I'm using the colosseum to gather 4 cards per cycle. By not progressing up the tower (which determines your colosseum rating), I can gather a 3x multiplier and sustain it long enough to gather 4 cards in 3 sessions. Each session can last about an hour as I can play 30+ hands before I'm out of options - low level common cards. By having a large health pool I can make synergised hands with 500 base damage defeat opponents with 12k HP. This allows me to play casually and still be succesful.
My goal is to collect at least 50% of the legendary cards before increasing my tower rating, which is about +15 cards from where I'm currently at. Besides, the cards you get for completing the tower aren't the best when compared to more recent premium sets.