To me Domino, Gwenpool, Magik, Morning and Mysterio.I think those will bring you diverse utilities... some hard hitters, bleeders, control power and some inmunities.Honorable mentions to CAIW (you already have hard hitters), Stealth (antievaders) and Sentinel (good inmunities).
I think (just personal appreciation) that it would make differences in higher tier levels. Domino is already awesome! Currently I wouldnt recommend capping two spots for improving one champ. I rather go with diverse utility and getting used to different champs and play styles through different nodes. A 4* Magik brought me to Uncollected