If the helicoil needs replacing, the likelihood is very high that there is some damage to the threads in the head, meaning a like for like insert replacement could fail. Therefore, the recommendation seems sound to me. The oversize insert will require re-tapping with an oversize tap as well. Even if the current insert hasn't failed, the operation for removing the old one is likely to gall the alum threads, also requiring a re-tap and oversize insert.
This is a recommendation I would follow.
Larry