First let's look at the two opposing arguments
Admirals are equal to Yonko.
Yonko are better than the admirals
Old Admirals (marineford):
Let's examine the major evidence both ways: Evidence for the Yonko is that Whitebeard fought all three Admirals at Marineford. Even old and sick he heavily damaged Akainu and tanked attacks from the other admirals. Shanks blitzed and blocked an attack from Akainu, ended the war.
The Counterargument is that Akainu almost killed Whitebeard. All three admirals got hits in and two of them were not injured at all. Whitebeard caught Akainu off guard. At this point, it seems like a fairly even matchup, and although the more capable and experienced whitebeard did serious damage, it's hard to say that he is much above the admirals. Kizaru was also confident he could stop Big Mom and Kaido from meeting, and he is not typically portrayed as stupid. Akainu is also a fleet admiral level (whatever that means) and the former Fleet admiral Sengoku was canonically one of the strongest men in Rogers era. Thus, on average, the Akainu, Aokiji, and Kizaru I would suspect are capable of fighting toe to toe with Yonko.
New Admirals (post-timeskip):
The new admirals are pretty mediocre in terms of feats. Fujitora and Greenbull failed to stop the revolutionary army from rescuing Kuma and they escaped unharmed. The exuse Oda gives is that they are in Marijoise. But imagine saying Kaido and Big Mom failed to stop or even injure them. Even using non-destructive attacks, a yonko should mess them up. Secondly, Greenbull struggled in Wano. Defeating King and Queen weakened means nothing, as does taking on a heavily injured scabbards. Brushing off Yamato's attack is decent, but certainly not overly impressive. I don't think we've seen all he can offer by any means, but it was pretty pathetic. I also don't hold Shanks scaring him against Greenbull, because taking on Luffy, Law, Kidd, Yamato, Zoro, Sanji, Shanks and his crew is unwinnible even for Kaido.
Conclusion:
Akainu will/should be a Kaido level threat. Oda has already foreshadowed this because Kaido's lava/fire body burned gear 5 luffy, and Akainu is the best lava user in the verse. As fleet admiral he can be a new age Garp/Sengoku. It seems reasonable he could push Luffy to his limit.
Aokiji should be on a similar level. Though I don't know how big of a role he will play. I want to see either a rematch between him and Akainu or him turing on Blackbeard and his crew. If he is a double agent Law fighting BB would be a great opportunity to change sides.
But neither are technically admirals. And I don't think there is strong evidence that Fujitora and Greenbull remotely stack up to the Yonko. I could see Sanji or Zoro or even Jinbe defeating them, putting them solidly below yonko.
Kizaru is weird, but id put him similar to Aokiji/Akainu.
So my current conclusion is 1 is somewhat true. Yonko on average are above the admirals, though certainly admirals should be able to match them.