To be frankly speaking I don't consider admirals weak. I still see them as strong as yonkou because yonkou class is weird in it's own way. Roger , whitebeard , kaido being top tiers , shanks , Blackbeard , Mihawk (not a yonkou) being mid tier , and luffy and bigmam in low yonkou tiers.
and for the aramaki arguement. I really don't think so bro was scarred of SHanks. translation says It's red haired pirates. He never names shanks. no yonkou or admiral is actually fit in the mind to actually challenge a yonkou crew alone. what aramaki did is what every top tier would have done if standing alone.
Admirals >> law and kidd definately .... for luffy It get's weird again as even among admirals there's a weird power gap. akainu obviously being in the top tier with aokiji, mid tier being kizaru and aramaki and fujitora in low tier cuz bro never uses his power aggressively unlike other admirals.
a feat which aramaki performed by takin down king and queen is like kaidou winning against all the supernova on rooftop with getting one adcoc attack from both luffy and zoro. and yet not harmed. and admirals downplayer really pushing an agenda ahead for their character.