Why not both?
Reduce tank healing at least to pre-EW levels. And increase damage so healers have more to do. It's not like fights having very low healing requirements is a new complaint...
The problem is that this assumes a tank soloing current full-party content is the problem. It's not; it's a symptom. If you make it so "Well now a tank literally can't solo it; they'd have to duo it instead", you haven't fixed the issues at the root.
Enrage would make DPS necessary, but not healers. I've already been forecasting that solo heals or no heals will be very popular this expac if design continues as is, outside of cases where mechanics may force 2 healers (eg healer-split-stacks in p2s, for instance)
