For the low short into fierce hands, I don’t know the reason, but it seems like it’s easier to get fierce hands out if you tap another button immediately prior to going for fierce. So for low short into fierce hands, it would be down+short+fierce-fierce-fierce-fierce-fierce. You have to tap it quickly, but not ridiculously quickly. I do index finger on the short and ring finger on fierce, and I tap the ring finger a bunch; obviously the ring finger isn’t the fastest one on your hand, but it still comes out most of the time. Pianoing doesn’t work in ST per se, but since it seems that fierce hands comes out more easily if you press a button right before fierce, you can tap strong-fierce-strong-fierce etc and either strong or fierce slaps will come out.
As for jumping short butt, it beats certain attacks if it lands on them, like it can beat/trade with parts of Guile’s low forward for example. It also cuts Honda’s jump short as soon as you press it, so it’s a decent way to move forward, especially if followed up by fierce hands.
If you’re going for tick into command throw, mixing it up with a jumping short butt every once in a while isn’t a bad idea. The best ticks into command grab are crossup roundhouse/forward splash into low jab, negative edge grab, but like with any ticking in this game, you need to mix it up. There are no real negative consequences to getting reversaled out of the grab because you’ll just block and be able to go for headbutt/hands/grab/whatever, but still, you’d rather get command grab than not, so mix up your ticking by adding a crouching short or standing jab or whatever, you know, just to keep the opponent on his toes in terms of when he should try to reversal.
On how to get around fireballs, it’s really character-specific, but in general your tricks are buttslam (not that good usually), jump straight up toward+fierce, walk up and block, jump toward forward/roundhousewalk up toward+roundhouse, and fierce hands dash (get fierce hands out for the smallest amount of time possible and it essentially becomes a dash). Not great options, but that’s what you have.