It sounds like you just got a bad group. Once the tank has secured agro, regen is fine to use since you know they’ll be taking constant damage (using it on dps is arguable, unless they’ll also be taking consistent damage). The only way medica II should be pulling agro off the tank is if you popped it right at the start of the fight, if you spent the fight aggressively overhealing, or if the tank is bad (applies to regen as well). As far as the sch telling you to not use cure III for geocrush, a well-timed cure III (i.e. spell fires shortly after geocrush hits the group) is by far the best way of getting everyone topped off.