You are exaggerating the size of the base bloom heal by a ton. (It has about 100k total, not per person)
Base bloom is on average (13400 + 124.2% sp) *1.10 (naturalist). If we assume say 50k spellpower, you get a base bloom of 83050. Lets assume a buffed mastery of about 30% and you get 108k divided by number of targets hit. So if you hit 10 targets the "base" bloom is only 10.8k per person.
By far the majority of the healing comes from the stored bonus healing (from rejuv overheals); the numerical value of which does not scale with int, mastery, crit or haste - only stamina/max health. The speed of recharge does scale with int haste mastery crit. Base healing accounts for like 15-20% of the total (assuming you max out the bonus healing)
Though the base healing does scale with int, i wouldn't ever recommend "stacking int" specifically for the bloom.