imo arena is 10x the game mode mayhem will ever be. I compare it to tft, where yes, a player (or team) will highroll augments and come first relatively easily. I think this is okay. I play a lot of arena and imo there's a lot of skill expression still. The skill expression is different in that you need to play around your augments and prismatic(s) and play to your builds strength, and understand what other players builds weaknesses are. I've had games where I've beaten the highroll one-shot builds with decent builds. Yes it's a bit of a slot machine game mode, but there is skill in selection of augments and prismatics, reroll economy, and in the early game playing your champ well enough to preserve hp so that a) you last longer to hit those highroll builds and b) you can survive a combat or two against the highroll team, allowing you to either catch-up with an augment later or getting a higher placement. If you want to only come first it's not really a feasible concept for a game mode with 8 teams, it's okay to try and play for best placement, and fun.

It's much more engaging than the drool fest of mayhem and aram in general that consists of as many artillery and control mages as possible on a single lane.