Only difference between admirals and emperors is that emperors got to show their full power during MF and WCI/Wano saga while for admirals it only happened off-screen in Punk Hzard.
Add that to the fact the series is about pirates, the MC is a pirate, and idealizes pirates and the casual reader will obviously view emperors in a more favorable light, even forgiving when they get countless anti-feats like Big Meme, get ragdolled by scrubbards for a whole chapter , or diarrhea shit their pants from a lone drunk cripple admiral or sensing the power a casual one lol.
Yet Oda made clear both the peak of the marine and the peak of the pirates are in the same tier. There's no fucking reason to put "defeat the admirals" as an equal requirement to surpass Roger's legend otherwise, beating the emperors should be enough.