A lot of people have something to say about Luffy running out of Haki this chapter. They think it means that he didn’t overcome the same limitations he had during Dressrosa or Whole Cake Island.
I can guarantee you that if Luffy used Gear 4 the same way he did vs Doflamingo and Katakuri, the ‘limit’ wouldn’t even seem to exist anymore.
The limit only exists because of Haki usage and expenditure. Luffy has never used more Haki than he has now. He also never had more Haki than he had now. All that happened is his Haki level went up and his consumption level is currently up.
It’s like mana in a lot of video games. You get more Mana as you level up, but that doesn’t mean you will always have more Mana. With higher mana you can more consistently use stronger attacks against stronger opponents. It doesn’t mean that you use access to the less mana consuming attacks you used to use on the way there though. You can still use those attacks, and your Mana levels will look ungodly for the level of attacks you’re using.
Luffy ‘gave it his all’ in the gattling he did. Was it his strongest move? Probably not. But when doing the attack he exerted an incredible ton of Haki into it which depleted his usage. Remember, essentially every punch was using Ryou, which essentially uses additional Haki and forces it into the opponent. If he were to use Gear 4 like he did previously, he wouldn’t be using nearly as much Haki in one go, and his increased Haki control/reserve would show itself.
I think what scares people is what Law said about 10 minutes. They are taking that information like it’s Oda telling us he’s going to be out for 10 minutes. Realistically, the last time Law saw Luffy using Gear 4 like this was in Dressrosa where he was directly involved in Luffy’s downtime strategy. Law wasn’t there to see Whole Cake Island and how much more control Luffy got over his Haki usage and recovery periods. So Luffy is probably going to shock Law by not actually being a complete liability for 10 minutes because he’s done it before, just Law hasn’t seen.