It's not just that. They are using a spell called mending splash I think. It has a 3 second cast time. They use other similar spells. PC clerics are using mostly their fast heals of various levels. Mercs are commonly using heals with very slow cast times, and combine that with they do not begin casting until the tank has already lost HP, I can easily go 3-4 seconds without a heal. This can be inadequate at times. Other times, and I may be wrong here, but I can crit a life tap or something and they stop their cast, only for me to get hit more. The mercs can heal well, and I'm just fine on singles. However, even though my DRU heals for less than my CLR merc does, my DRU beginning their cast before my SHD takes damage can make a big difference. The thing that bothers me about my DRU is that Clovida lands for 200k at times, and at a 3sec cast time, that's very bad. I played a CLR for a long time and was shocked at how much I overestimated DRU healing and Merc reaction times. I'm not expert, and I am a terrible SHD, so I could be wrong on all of the above.