Admirals represent the power of the Marines. They represent the main military force of the WG. It would make 0 sense that the Marines downgraded their main power over the time skip, while every other faction upgraded.
Logically, if you're the strongest in history. The individuals that represent your power would be the strongest in history as well. Normally how it works in manga.
Sengoku didn't trust in Admirals to win the battle vs WB only, the new PX Army made him say ''victory'', Admirals weren't enough.
Obviously, Admirals aren't the only factor.
Vegapunk's new help to the Marines during the time skip, as well as lower ranks getting stronger could be the reason. Jinbe never mentioned new Admirals strength, he just said the Marines are stronger for some reason thats it. That can be speculated easily.
They even gave up on Shichibukai, because SSG and Vegapunk's weapon got stronger.
Not because Admirals got so much stronger they didn't need Shichibukai anymore, Fujitora literally said its because of SSG not because Admirals are stronger now.
Makes zero sense. The admirals represent the strength of Marine HQ, so if the admirals were weaker, then Marine HQ would be weaker.
Kizarus not stronger than Fuji and Ryo
Which Admiral is stronger than the old one?
Akainu replaced Sengoku
Ryokugyu replaced Akainu
Fujitora replaced Aokiji
Sengoku > Ryokugyu
Aokiji > Fujitora
At best they are equals, which I highly doubt.