I think there's only two ways they can alleviate this:
1. Retune stats for older content to be balanced in the way they were intended and compensate the iLevel difference and level difference (maybe stat caps)
2. Give us better DPS options because that's all we are going to be doing anyway.
After clearing Titan Savage my group decided to do Cape Westwind min iLevel synced for fun and the healing experience was more intensive, I think when you play some of this content at a level it was intended it's more engaging.
I don't think it will be perfect as I think encounter design plays it's part too, but I think it would ease the problem. And I think it'll be good for newer people too because they get to enjoy the content as it was intended instead of just face rolling stuff like it's insignificant
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And despite having pushed a lot for option 2, I think I'd actually prefer option one in this content (well, actually both, but I know it's not going to happen) and I don't think it would be a bad thing whether you're doing the first time or as part of a roulette, because when you're doing something for the first time, it improves your experience if you're doing the content as it was intended and get the full experience.
And if you're doing it in a roulette, in each of the roulettes you still get on-content stuff and people who're not highly geared. So does it matter if other instances take just as long? Especially if they adjust the rewards to compensate (eg. exp in a levelling roulette) like they do between Castrum and Prae in MSQ roulette.
And imagine doing mechanics in Labyrinth of the the Ancients again or doing the door mechanics at the end of City of Amdapor (which you can just heal through now) and so on. I feel like facerolls are what undersizing is for.
So it'd be more than just a benefit to healers but to other roles. And the bonus is if the end result is that your healers are focusing on healing more and avoiding letting health drop as much (where a certain percentage is still enough to survive an AoE or tank buster) then the issue of people dying due to healers DPSing would be alleviated. It won't be solved, but then it won't be solved because people will strive for optimal play, but at least they're less likely to tunnel vision and be a little more on their toes.