part of the problem is most the healers that do that either dont know what enmity/agro is, or just plain lazy.....there is almost no reason at all for them to cast regen at the end or beginning of a fight. if they want to top you off, they should use cure or adloqium (idk if thats the right spell, but idc either) or let it automatically recover.
me personally, when i do heal, i always top off the tank at the end of a fight and then pop swiftcast + stoneskin.....but im also not a lazy healer and normally dont pull much threat since i try to avoid overhealing, and just use stoneskin to help with mitigation too, and i usually use more than 4 buttons when healing in most fights, including trash mobs