Personally Universal/Universal+ for DC/Marvel Heralds should be consider a possibility, at least when it come to genuine feats and not take out of context (like Hal Jordan holding the "Big Bang" or Post-Crisis and Golden Age Supermen were "destroying" the universe in their clash).
While there may be Universal/Universal+ feats between the many inconsistencies/retcons, character's holding back their strength or their powers vastly change across stories it just too difficult to be sure if those are legitimate or just outliers.
If i'm going to be honest, i think the best way to tier DC/Marvel characters would be with having a Varies, where their most consistent mid-high end feats should be their principal tiers, while their best high end feats should be left as possibly.
So something like this:
Marvel) Varies. 5-B to 4-B, possibly 3-A/Low 2-C.
DC) Varies. 5-A to 4-B, possibly 3-A/Low 2-C.