Video games should equal fun. Many healer mains are not having fun. Healers are often unneeded in certain scenarios, which is frustrating. No group content in a trinity-system-based game should be easily cleared with part of that trinity system missing.
How this issue will be fixed is up for discussion – there are quite a few feasible options to choose from.
The problem first needs to be acknowledged by SE, and they need to tell us what options are on the table.
Only then we can have a real discussion.
If you knowingly accept the fact that an important part of the player base feels unneeded or unhappy, then don't be surprised when the game as a whole suffers in long-term as a result.