Did Luffy have Snake Man against Doflamingo?

[ahill1]

...or was that something he just developed as the time advanced?

If he had it against Doflamingo, why wouldn't he use it to end the fight quickly?

 

[Captain Cadaver]

...or was that something he just developed as the time advanced

Could go either way, though I'd assume he developed it during his training seeing as how he didn't say to Katakuri he developed it to combat him like he did when talking to Blueno about developing his Gears to combat Blueno. It seems like something too specific and technical for him to come up with one the fly. Then again, the same can be said of him asspulling Gears 2nd and 3rd at Enies Lobby out of nowhere, so it can go either way.

If he had it against Doflamingo, why wouldn't he use it to end the fight quickly?

Same reason he didn't use Boundman to destroy the Noah; because Oda hadn't entirely written himself into a corner yet.

Seriously though, it's probably because Snakeman is a glass cannon due to it's Haki not covering as much of his body as Boundman and Luffy wouldn't want that going up against a tricky opponent like Doflamingo. He only used Snakeman against Katakuri because Boundman had already been countered, after all.

 

[sei'taer]

Luffy didn't have any issue keeping up with Doffy, he just couldn't actually hurt him and gear 3 was too slow.