One other thing to mention is that sometimes assisting with weak heals is actually a detriment to the party.

When my FC was first doing Titan one of our BLMs would keep spamming Physick on himself whenever he took damage instead of letting the healers handle it, which caused several wipes during the heart phase till I noticed what he was doing.

I can't think of any fights in FF11 except that Snoll fight and the Tenzen fight for CoP that required you to kill something within a time limit.