Lifebloom was supposed to get nerfed, but Blizzard didn't want to screw up PvE healing. I hope I have a solution.
Reduce the +healing benefit of instant casts by at least 50%. Make them really weak. To maintain raid healing output, buff heals with a cast time. The combination of these should keep raid healing output and efficiency the same. In PvP it will foce druids to make a harder choice between mobility and efficiency/output. Staying still makes them better at healing, but also vulnerable to interrupts and damage, just like any other healer. Going mobile gives protection, but with lost healing.