Melkor/Morgoth was the MOST powerful being ever in Arda and Sauron was his greatest servant.
Illuvatar spoke...'Mighty are the Ainur, and mightiest among them is
Among those of his servants that have names the greatest was that
spirit whom the Eldar called Sauron, or Gorthar the Cruel.
Each group has its own innate abilities. The Elves have greater control over their bodies and are therefore harder to kill and are more enduring of hurts than Men. The Ainur may take on physical form but they'd have as great a prowess as any Elf physcially.
In Morgoth's Ring when speaking about reading the minds of others a note says "all rational minds/spirits deriving direct from Eru are 'equal' - in order and status - though not necessarily 'coeval' or of like original power." Every spirit is equal but not necessarily in innate power. I liken it to people being equal under the law, but of varying abilities.
It is also said that the Ainur themselves "become more impotent" as the shape of things in Arda become more defined [Morgoth's Ring; Myths Transformed]. This will occur even with men when "they have completed their function". The Ainu are spirits, but the Elves and Men also have spirits living by a union of spirit/body. In Athrabeth Finrod ah Andreth it's said "the fëar were not spirits of a wholly different kind to the Ainur".
The Ainur would be greater in innate powers than Men because that's how they were made. Elves have taken out Maiar (Ecthelion/Glorfindel/Gil-galad) but as far as I know this would be beyond Men and yet there are Men who have beat Elves. I should point out that Gil-galad and Elendil both took out Sauron, a weakened Sauron, a Maia nevertheless. In that instance even a Man was able to take out a Maia. In Aman it appears that even Feanor was able to use his voice to overpower a Maia messenger:
In that hour the voice of Feanor grew so great and so potent that even
the herald of the Valar bowed before him as one full-answered, and
departed; [Of the Flight of the Noldor]
This is a power that reminds me of Saruman himself.
There seem to be discrepancies where you'd think Elves having more innate power should always be able to beat a man, but this is not always the case, or a Maia should always be able to overcome an Elf or a Man but this is not always the case. Feanor, however, was not normal and quite mighty. Weapons might simply mitigate these innate power differences between people. As seen with Fingolfin in his battle with Melkor. Yes Morgoth was weaker than he used to be, but he was quite a beast in terms of innate powers. Yet, Luthien overcame him, part Maia though she was, and she also put to sleep most of his other Maiar servants, but Sauron nearly took her out on his own before Huan saved her.