How rare are persistent iOS malware exploits via Safari?

You really don’t have to worry about malware on iOS like that. It's extremely uncommon for exploits to stay on the device after a reboot or an update.

It's almost impossible. If you get hit by a Safari exploit, an update would typically wipe any traces of it completely. Updating your iPhone usually keeps it secure!

I agree, it's extremely rare to see persistent malware like that. You should be safe unless you’re doing something questionable.