What's good for the goose is good for the gander. I would say the obviously disqualified picks are SRR, Monzon, Greb and Hagler. Hopkins would be just a step below.
Holman Williams. If his era wasn't quite so stacked (and more importantly, if Cocoa Kid did not exist), he would have been there at Mt Rushmore instead of someone like Hagler or Monzon. Best winning resume at the poundage, arguably. Charley Burley x2 Jack Chase x4 Lloyd Marshall x2 Cocoa Kid Aaron Wade Bert Lytell Eddie Booker Jose Basora x3 Steve Belloise Kid Tunero x3
Holman Williams got a shot to fight for duration title but it was draw with Cocoa Kid and duration titles were ended soon after. I think earlier fights might have been supposed to be for duration title but either him, his opponent or both missed weight. A big problem with putting Williams in a MW GOAT conversation is a lot of his fights weren't at MW. Of the wins you've listed this includes Burleyx1 Jack Chasex2 Lloyd Marshallx2 Cocoa Kid Aaron Wade Eddie Booker Kid Tunerox1 This also includes a draw with Lytell and some wins over other notable opponents a tier below the ones listed. If these guys were HWs that would probably boost Holmans case but this is the core of his would be resume.
Coming a few lbs over the divisional limit was common practice in those days for non title bouts. Those guys were ranked at Middleweight and would fight guys who usually weighed around the 160 limit. Thus, they should be treated Middleweights. I'm not gonna classify those wins as Light Heavyweight wins just because Jack Chase came in 160.5 in one bout and at 161 for the other one. Or because Williams came at 161 against Tunero in 1 out of 3 fights. I guess I can give you Lloyd Marshall (barely), but definitely not the rest. Anyone who was ranked at MW and consistently weighed below 165 or so is a Middleweight in my book.
But I'm saying this likely cost him the chance to be a champion. Thats a fair interpretation. The way I see this issue is you get credit for beating another notable at the weight class no matter what but the fight doesn't count on your WL record for that division. Open to rounding but either way officially that makes fights ineligible to be title fights. Lloyd Marshall was a LHW champion ranked at LHW not MW when he fought Holman Williams. Its a good P4P feat but Marshall was a MW/LHW combo fighter. Sorting combo fighters into weight classes by association when they aren't making weight is tricky though. Booker was ranked 1 year in LHW and MW each. The rest you're right. The thing with considering anyone shorter than 165 a MW is historically MW was smaller than 160 not bigger. I would have much preferred MW and LHW be raised 10 pounds to 170/185 to creating tweener divisions but thats another story.
I'll say James Toney. While Middleweight was never his best weight and he doesn't have a lot of fights at the weight he actually has some great wins at Middleweight: Nunn, Johnson, McCallum x 2 (I thought he won both fights) and Sosa pretty solid resume imo
The old site Cyberboxing Zone was SUPER high on this guy. If anyone remembers Gordoom the moderator. He had him ranked above Sugar Ray Robinson & Hagler. So I would say he's the Ultimate Darkhorse champion. What the thread was after. Gordoom ranking at Middle 1) Greb 2) Monzon 3) Cerdan 4)Robinson 5) Hagler
Don't forget he beat Archie Moore. What an insane resume. Surprise he didn't fight Ezzard Charles at all.