My last game with Omu I had a Chef Nomi on turn 5 and took an Elemental build to 1st. Bob was nice to me right from turn 1 (2x sellementals).
I find usually that I focus on stats early game and the right trade offs to level at the optimal times. Then I try to get some sort of mid-game build synergy going often instigated by a good T4 card. But I am looking for the T5/T6 cards to shift to whatever late game build I can. Of course Bob often misdirects me with one good card then nothing more.
You can finish top 4 a lot with a strong mid game build < the top 20% MMR, but if you want more 1st place finishes you need to be looking to transition to a solid late game build as early as possible and/or get lucky. But I find the top finishes often come when the late game build leverages my mid game.
The higher your MMR the better you have to be at the late game. Unfortunately your low MMR games don't really teach you to emphasize on this. You kinda have to make your way up then ask yourself why you keep losing now. It likely comes down to 1) not properly focusing on stats and the optimal leveling points early and 2) you really haven't learned the art of the late game yet.
But Heros do matter huge.