Rogue Val’s AoE heal helps keep everyone else around her up - until she is focused enough to pop her own heal burst and that goes away. In actual combat her chain medgun is not really enough to keep a single focused hunter alive - there you rely on shields, kiting and damage pressure. So it’s really her AoE aura that does the bulk of her healing, at least in legacy.
I’ll also note that Rogue Val encourages a far more aggressive play style because of her poison darts and need to keep allies within her AoE range - it makes you want to keep those active at all times. It is very possible that when playing Rogue Val you are getting closer to the Monster than otherwise, and that is resulting in your getting focused more easily.
In general though, the medic and support are always the key links to keeping the team alive, and unless a Sunny is in play I tend to focus the Medic first. If the monster focuses a target, they are MEANT to go down eventually - the role of the team is to keep the focus up as long as possible, and punish the monster throughout. Trapper CC is meant to slow the monster enough that the focus can get away, shields and heals keep them alive, and the focus themselves needs to kite and dodge effectively to break monster combos. Absent this teamplay, an individual hunter is meant to go down fast, and two together won’t last TOO much longer - so to say medic is reliant on a good trapper/support pair is probably going to be true in any case, Rogue Val or not.
In Stage 2, her AoE heal combining with hunter passive heals and possibly further combining with a hunter regeneration perk… yeah, I can see why she might need some adjusting.