I think you may be taking more mixups than you need to. Alex has actually very few true 50/50 situations. Here are a few things you may not be aware of:
1. After he hits you with his command grab, his next mixup is NOT a 50/50. His dash up command grab hits at a different timing than his meaties (elbow/st hk), so you can fuzzy guard it. The dash up command grab is also not only negative but unsafe and full combo punishable if you guess he's doing it.
2. Blocking a f hp is a free v-reversal punish. Save your v meter for this. It's only a 50/50 if you have no v meter.
3. Many characters have a move which can cover both the j hk and the dive bomb, so he can't use that as a mixup. Reactive air to airs also works for a number of characters. If he's not mixing up these two, and you're just struggling to anti air j hk in isolation, I think you just need to practice it, it should be fairly straightforward.
There's more stuff too - lab him and find out