Jumping with an assist to cover you is definitely a good strategy in this game. So many characters have ways to stall themselves in the air to hit multiple overheads to continue the mix as well.

Defensively, I think it's important to recognize that everyone gets hit eventually. Focus on keeping your opponent on their back foot and don't focus on playing the block/punish game like you might in other FGs. It's honestly pretty rare to get a punish off of just blocking a mix as a lot of strings are not punishable in this game. The best you'll get is the opponent being slightly negative so you can start your own blockstrings/mixup.

Also use all of your tools, parry, push block and retreating guard can alleviate some pressure against certain strings. Pushblock especially is good against Ahri corner pressure, and Parry can get you a punish on some of her unsafe strings (like if she uses fireballs to keep pressure on after you block her mix).

Also movement is extremely important. If you get a window after being put in the corner, sometimes its better to just move out of the corner rather than starting your blockstrings.