Look how Tanak stagnated in Hyundai, especially on tarmac where he is now regularly the slowest Hyundai. Right now he can at best get 4th in the championship. Brings some perspective.
Does that prove Tanak is a level below or that he is on the way down?

Before that in VW Mikkelsen was clearly on the way up, slowly compared to say Rovanpera, but he was. In Rally2 this year there was a clear change of approach after Sardinia and then a step up from Estonia onwards. Note the Dirtfish article saying he needs to step up and win rallies before Greece, since then he won all 3. So downward trajectory not so much , more like up and down. Note that he is same age as Breen and their number of starts in rallies is starting to become similar ad well.

Thing with Mikkelsen is that he never was a driver that wins many stages by large margins. It's always "steady pace", once he gets some gap he starts controlling it rather than pushing on. ( see Estonia this year, Greece, Fafe). For some this shows that he "barely" has the pace to win. "Mcrae/Meeke" style of winning one stage big then crashing on next is more popular, even by team bosses, just look at Solberg, Lukyanuk or even Fourmaux.