Im going to comfortably pick Tiger Flowers. If you weren't a big puncher Flowers was going to give you problems. Williams was not a big puncher. Consider this: Flowers turned pro in 1918, for 7 years the only fighter who notched a decision win over him (it was a newspaper decision) was Greb. It was almost ten years before anyone won an official decision over him that wasn't heavily disputed and that was Lomski and even that decision was disputed to some degree. Flowers also had a style that would have driven Williams mad. Flowers was kind of like Greb in that he was very fast, had a lot of stamina, and threw tons and tons of punches. The question about Greb in these matchups is "how do you beat a guy on the cards who piles up millions of points if you cant stop him?" The same question can be asked of Flowers. I don't see Williams stopping him so it goes to the cards and I think there Flowers would have a significant lead.
I concur and pick Tiger Flowers too. He was so difficult to outpoint as like Greb he threw so many punches. Add to this Flowers was a southpaw, and off the bat we know southpaws have an advantage over orthodox fighters.Leo Lomski who you mention was a terrific hitter who came close to flattening Tommy Loughran...The great boxer/puncher Jack Delaney had Tiger Flowers number koing him twice in a row. Years later there was a fighter named Tippy Larkin a lightweight who I saw who in over 120 bouts was almost impossible to outpoint, but had a glass chin that saw him being kod only by "bangers", like Al Davis, Beau Jack, Lew Jenkins, etc...
Foot work and defense often negate swarming...and a prime Williams based on his record would have those attributes...but I tend to agree that Tiger would take a decision win...but I'm thinking it's closer than Klompton and Bert suggest...