from those i'd say Eliot,Kokoro, and Brad are his easiest matchups
Eliots damage output plummets against super heavies where he can't take advantage of his instant 3p refloats on them at all other than from his throw launcher while Leon can destroy him off any of his launches with him being super light weight. Leon also has faster mids and can beat him out up close where only eliots highs outpoke him which are easily crushed by 33p
Kokoro is in a similar position as eliot in the match up but with faster mids, but due to her short strings and lack of tracking Leon can easily step her offense without much trouble and maximize his damage on her due to being light weight where she can't against him.
Brad is one of the few characters who Leon is faster than so offensively he can out pressure him and his lay-down stance shenanigans easily gets stuffed by low OH's
all 3 of the above have average damage output to begin with but when pitted against a super heavy that average damage becomes mediocre damage vs Leon's highest damage output in the game. none of the above 3 have the zoning tools to keep Leon out which as i mention before is his biggest weakness so they pretty much have to come in close where Leon is at his best and can either match or exceed their close range pressure while dishing vastly higher damage to them in the process
Okay, so which characters do you think he's at disadvantage on?