YJ-12, YJ-18, and YJ-21 are pretty formidable offensive weapons.
AGEIS seems to do well defending against it, but Taiwan itself doesn’t have a robust anti missile capabilities like carrier groups.
A lot of faith is put into the SM-3 system for high altitude intercepts. Thankfully it seems like Japan has some SM-3 capabilities.
I also don’t think they’re willing to compromise their own shipping channels for the sake of taking Taiwan. I have a vested interest in Taiwan as half of my family lives there.
I also believe that China has India to worry about as well. Not commonly discussed but still a valid threat.