Make it so that upon recieving a heal, DR or DP is increased for a short amount of time 

Ex: +30% DR or +200 DP for 1s after being healed.

It's almost balanced in 1v1 situations for classes like Witch/Wizard.  With maybe the exception of Succ Wizard because of the double teleport.  In general you CAN'T just heal up in a 1v1 fight.  It takes to long and will lead to an immediate CC.  This leads to trying to time smaller heals or canceling the full heal.

The issue though is that it doesn't really work very well due to increased mobility of far to many classes and because grabs will simply break everything.

Yeah, Kinda was unclear, but the purpose is for mid-combat heals that are supposed to be for assisting allies. Currently it's kind of pointless using them because 99.9% of the time you're better off just CCing the attacker(s) because in the time you spent healing the ally, they lose more HP than you heal.

I do get your point and it could be resolved somewhat by that method.  However, it could also be resolved by group content lowering the damage substantially so the heals would be more effective in the first place.

Pearl Abyss already tried this with the bonus HP.  However, it's probably better to just adjust the modifiers for RBF, Nodes etc.  In those situations there is an expectation that you are supposed to be in a group fight.  That means you don't necessary need enough damage by yourself to kill an opponent.  You should be working as team to focus on specific targets.