After you land you have enough time for a throw or his "instant" overhead. You can't get anything off of the throw without an assist or xf though,except HCS, and comboing from the overhead requires strict timing.
Unless I'm misunderstanding you, this is insanely unsafe. Captain is very unsafe without assists. Most people don't know how to punish him though. Literally 90% of the screen is a deadzone for him so if you have ANY option from those ranges, they're better than him.
Throw a shield from long range- can't convert.
Throw a shield from short range- they block it and then have time to punish you before your shield comes back.
Do a raw cartwheel, get punished since you're vulnerable for like 20 frames. The only way I could see this possibly working is if the shield is coming back to you while you're in the middle of your backflip, but even then they can just touch you and your shield loses its hitbox. Captain is a terrible anchor. Not because he can't kill you (if you get touched or thrown, you're probably going to die), but because he has very few options and almost none of them are safe.