Luffy's stamina issue is a plot armour for all of Luffy's opponents in the NW.
Luffy was killing Doflamingo in Gear 4 stopped by stamina.
Luffy lost stamina against Katakuri numerous times if he could keep up Snakeman he'd have beat him easier.
Gear 5 Luffy is OP and can arguably based off this chapter low to mid diff an admiral if he hits his attacks with AdvCoC.
The stamina limit is clearly a plot induced restriction placed on Luffy to stop him neg diffing a lot of opposition and to keep up the underdog role Oda wants for Luffy