I’m in a somewhat similar situation. I have both Viv and Ranvir. Darts are rare (F2P). My alliance fights even smaller titans (3-4 star max). Before I had Wu, I took Ranvir to 2^60 (8/8) to try out on titans. I was unimpressed. The damage boost just didn’t seem to be there in as great a magnitude as I anticipated. Now, I have maxed Wu, and he has completely replaced Ranvir on my yellow titan team, since his base tile damage at 4^70 is better than Ranvir’s at 2^60. In fact, I forget I have Ranvir on my roster most of the time. Literally haven’t used him in months.
OTOH, I took Viv to 3^70, because I usually try to run two healers, and cleanse is a rare skill. She does her thing at 3^70, but the problem is her slow mana. She’s often dead before she can fire. She got my most recent set of darts, and now sits at 4^65 and climbing. Durability is much improved, and it’s now much easier to raid 3-2 because I have at least one healer in every color. She gets out a lot more now.
Bottom line: Ranvir is an expensive Wu clone that you really only need if you fight high level titans or if you are desperate for druids (which I was, at one point). Vivica is the only classic 5-star healer, and until recently, was the only yellow healer, period. She’s also one of a very few heroes to possess the cleanse ability, although costumes have remedied that a bit lately. So, is she the best healer, the best cleanser, or a must-max hero for everyone who has her? No; no, she is not. But she’s one of a very few who can do what she does (in multiple categories), and that’s been more than enough for me. Darts well spent, and cleric emblems on the way when she reaches max (although part of that is that my non-Rigard clerics kinda suck.) Good luck.