If something like this happens, I either turn my defensive stance off and go full dps when I'm tanking (and I won't use any CD) or vote kick the SCH...or I just leave the instance, I'm not there to carry their ass.And if you REALLY want to slack off, just go Scholar, summon your fairy, and autofollow someone.
Unfortunately healing in a non-raid environment is really trivial in this game and maybe for this very reason there are a LOT of terrible healers that have no idea how this game works or what they're supposed to do to effectively support the party other than just healing.
As for HoTs...well I've seen WHMs casting medica II and regen before the pulls for whatever reason, if that happens I just tell them not to do it, but luckily enough this is happening less frequently to me now. Always try to explain to them that applying hots before pulls is a very bad habit for a healer. If they won't listen, just let the mobs eat them and /laugh at their corpses.