It would 100% encourage 1H3Dps in speedruns because whatever does the most damage is what's most important, the main reason why 4dps isn't dungeon meta is because you still need some level of sustain and survivability just not much hencec why you don't need 1/1/2 you just need any 1/3 comp.
I've also said at this rate a thousand times over tanks should give up self survivability and mitigation and some sustain if you even read what i said in the other reply I mentioned that tanks need to give up a bit of their value in mitigation and sustain instances but this should be alongside some wider changes like increasing how much damage you take from all encounters.
I haven't suggested simply changing nothing, I've suggested it isn't tank's having some forms of healing that is the actual issue with healer's it's very easy to point at, because people think "oh hey tanks are doing my job, the way to fix that is just to remove tanks being able to do that!" without actually maybe considering that isn't really a proper solution, your instead punishing tank players for having those tools by basically wanting to fully remove one way a tank can support a group.
Tanks shouldn't need to give up core abilities to their identity so "healers can be fun" if a DPS is performing well we shouldn't just remove it's burst damage buttons, we should scale down its damage, if tanks survivability and sustain are too strong then we should scale it down, not remove it entirely, I don't get how this is a hard concept to understand.
Scaling down tanks proportionality will always be a better solution then just removing sustain & target healing. also stuff like making bosses and AOE do more damage, making sure gear scaling doesn't make any content trivialised, giving healers more to do in downtime (yes healers don't need just dps buttons but extra dps buttons are also something that would make them more fun). All this would make healer play and feel a lot better then just blindly removing sustain and calling it a day, which again is a lose/lose.