Pre Crisis Fate had the strength of Post COIE Superman not pre. He had super strength and invulnerability( except his lungs - he needed to breath) without the helm courtesy of Nabu's alterations to his DNA but he certainly wasn't a planet mover. He carried air liners and such but that's it. He also had nothing above sonic level speed where his physicals were concerned. His magic was IMO slightly behind Classic Strange ( only slightly) but was made up for with his other powers like the physical ones mentioned and his energy manip ( throughout the Golden age he used the power in his atoms or controlled electricity, fire, or any other form of energy around), and his TP and TK ( best feat I can recall was moving a planet into it's sun)
If we take the events of the Grey man saga ( which was post COIE and after the Legends mini series but still Kent before handing over the mantle). Grey man defeated Kent and was then taken telepathically by MMH. So on at least one front there is a way to attack Kent by the JLA
JLA have a distinct speed advantage. Both Superman and WW are faster than Powergirl who based purely on statements is faster than Captain marvel. MMH is also about even with her.
JSA do win but I wouldn't say that fate solos. It would take two of them working well together to take him and likely would for Sentinel as well. The problem is that Whilst Superman will beat CM and WW will beat PG ( as both have before) it wont be before the other two are beaten and they need them to take down the two big honchos of the JSA.