Difference is Luffy is a zoan not a paramecia. Where did those special zoan awakening traits, regen, toighness wander off
Look at Lucci, even imperfect awakened zoans like jailer beasts last more than that.
Luffy is a Mythical Zoan. We've already seen with Marco that they function differently, as the more Marco used his powers, the more it drained his Stamina.
That makes sense, because mythical Zoans have special powers that regular Zoans don't. It's too much of a buff for them to have special abilities, and the same benefits as regular zoans.
If Marco had the same stamina regen as regular Zoans do, he'd be unbeatable as it would would make his healing infinite.