Um...correct me if I'm wrong, but I didn't think any characters could combo off their U3. It's just a "get off me" move. U2 is the universal wake up launcher.
"other then with Cassie’s back to the corner " I was hoping for a secret U3 combo when Cassie is in the corner and the spacing is special I was probably fool.
Btw U3 into pressure/throw can be still worth that bar especially in case of crucial gaps (and can not be punished with normal). Gaining the momentum, etc.
90 damage for U3.
With throw it is 230. With F4-F41 follow up it can be even better.