He has higher Tenacity in higher Tiers. Anything that does not do damage, but is not evaded, is a bug. I think it is doing damage. Try improving your Vader as much as you can, you will see better results.
Use QGJ lead. Over a long battle, he will gain the team many turns. There is no evidence to support that the Lumi/Ahsoka lead abilities are granting ANY dodge at all.