More like 3-4 skulls, at least.
4 skulls? No one who has actually used this feat will believe this.
This isn't taking a character barely getting through r6s to r10 level. No. Do you even play this game or just troll on the forums?
That's a massive jump in difficulty that this feat just doesn't cover.
Even an r1 to r5 jump isn't happening off the back of this one feat (that you need to burn 2 slots to even get).
And it'll matter even less in group play because it'll typically be a mix of healers, casters, melee, ranged, tank, etc all fulfilling different roles, plus many builds can just heal each other. Maybe it cuts down on the healer having to be nanny to people on low or mid skulls but it's not like any build can take this then wade into the fray, expecting a few hundred temp hp procs every 8 seconds to save them. You still have to play well in challenging content. There are far greater game balance issues that I've already detailed.
An r10 doom getting 1-shot from afar is clearly a lot more broken.