Totally possible even in lastest DSR ultimate, but your dps will need to actually doing real dps. Good dps healers deal around 4k dps on dsr. If you only put dots and heal and shoot sometime you are gonna be around 1.9k.it's 2.1k different. if 2 healers do the same so it's just 4.2k diffrent. each dps has to deal 1k more dps which is totally possible. I had a clear with only 2 healers are above avg and all dps were under.

welp to be fair it's much more easier for healers just do more dps to get the missing dps than dps try to milk more of their dps.