No way is Umesh Yadav better than Bumrah in any conditions or in any format.Umesh outside the rough wickets of India always struggles though. His action just does not lend itself to consistent line and length bowling, at whatever pace. And he has lost pace now. So its very rough. The only plus with him is reverse and he does not have that here and generally in T20s anyways. He is still a great bet in India for tests as the second seamer (Shami being the only one who is clearly better in those conditions) but otherwise, its tough to keep him around overseas and even at home for LO cricket.
Shami has similar problem of often drifting down leg naturally due to his action but he seems to have worked very hard on overcoming it. He still does it now and then but it is far less frequent compared to Umesh. And he was the better bowler even before when both had the weakness. Shami's action is less prone to falling apart than Umesh's, basically.
Imo