You'll absolutely want Doom and Corvus 5*'s at r5 in the long-run. I would prioritize Doom normally, but consider Corvus for this rank up since you already have the r4 Doom. With Corvus up higher you should be able to burn through some content to get the rankup materials for both of them.
With those two 5*s and Namor (when he awakens) I personally wouldn't invest much in ranking up 4* champs.
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With those two 5*s and Namor (when he awakens) I personally wouldn't invest much in ranking up 4* champs.