I’m newer to Adon, but I always use u2.
I use U2 for:
Honda: You can only punish heavy headbutts with U1
Blanka: Only get 3 hits for a reversal Ultra 1
Bison: Either U1 or U2 depending on the player. If they are teleport happy
Chun: Same as above but with fireballs
Oni: Because ex will dive punishes fireballs and U2 does good damage on him
Evil Ryu: Same as above
Ken: Most good kens don’t really use fireballs
I hope that helps in why I don’t use Ultra 1 with a lot of characters 
against Blanka the full animation can be done, its just timing specific! someone did a video before which shows that it can do the full thing. I would imagine the timing would be stranger now that they changed how blanka recovers!
Have to look into it. Cheers