I'd consider it more "legit" in training, where you can't double counter breaker before the moves leading up to the first ultra.
Practice is like the lab where u try and discover how high u can get. It's considered legit if no counterbreakers are used. I've seen 1000+ combo's where shadow meter is set to infinite or u just time counterbreakers against cpu. Set ur meters on refill is the same as normal, it doesnt give u an advantage while doing the combo.
Anyways in practice u can do the combo over and over, but online is a different story, u have to win, all meters must be full, opponent can break u in the combo leading to the ultra, u can drop the combo during the ultra and there is input lag. I have been trying for weeks to get the highest combo in ranked. It's tough!