[pacaro]

It feels ugly to me, but there doesn't seem to be a concise alternative.

It's usually used to refer to a person's record of wins, as in the coach who has lead a team to more wins than any other coach, at which point they are the winningest.

He's the...

winningest coach

most successful coach when measured by how many wins

coach with the best win-loss ratio

¯\_(ツ)_/¯

[cik2e]

“Most winning” would be the correct alternative, with the same number of syllables although to me it does feel more concise. As an American, I also hate this made up word.