Yes, while ever you're not in "end game" territory rank up anyone you can - I assume you have no 4* champs yet?
As soon as you get a decent stack of 4* champs concentrate on those and your 5*s and 6*s will follow
I have some 4* like x23, sabertooth,cave and hela actually because I was lucky with my PHC . I have heard that drax unduped is not so good because he can't stack furies.
Drax is only really any good for his bleed abilities, but if you have x23 and sabertooth I would concentrate on getting them to 5/55 before him in which case.
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As soon as you get a decent stack of 4* champs concentrate on those and your 5*s and 6*s will follow