When enabling this new protection, could we potentially disable other mitigation techniques which become redundant and therefore re-gain some performance?

Yes! The numbers in the posting don't account for this.

Before doing this though, you need to be sure that ASI actually protects all the memory you care about. The version that currently exists protects all user memory but if the kernel copies something into its own memory it's now unprotected. So that needs to be addressed first (or some users might tolerate this risk).