Regarding the whole "Does Haki influence fights" discussion, I've been thinking of Doflamingo. Doffy is a string man, whos established main deal is doing puppeteering or razor-wire slashes with wires generated from his hands. I don't know that any of Luffys fight with him really involves countering that, specifically? Like, theres no grabbing hold of the strings to drag Doffy, no following them to find the real him or setting them on fire or targeting his hands or like a weakness where he leaves himself vulnerable if puppeteering too many things due to it using his hands.
I'm thinking stuff like "Arlong shoots at Luffy like a high-speed dart, but Luffy makes a finger-net to intercept him", which could now be countered with "Luffy uses CoA to block"
There is creativity on display in the Doffys fight with Luffys development of Gear 4, but…with gear 2 and 3, these were developed as specific counters to the speed and durability of CP9, which was strongly tied to their concept of highly trained martial-arts assasins. Whereas Gear 4s powerup of punching even harder is a counter to a string man, because in addition to being a string man Doffy is ALSO insanely durable, simply as a byproduct of the scaling of the haki concept.
Or in other words, couldn't you slot in Gear 4 as a "solution" to pretty much any high level opponent with CoA?
I don't think there's ever been that level of exploiting possible Devil Fruit workarounds in the series, pre or post haki. People weren't trying to superheat Crocodile to turn him into glass, or set up ground rods for Enel. The water weakness or rubber vulnerability were just for establishing why Luffy could eventually punch the bad guy really hard. Most of the fights in the series have come down to speed and durability, at least Gear 4th utilizes the fact that Luffy is made of rubber.
I hate the idea of Im immune to your power because I'm strong. You should have to work around it. It's fine for haki to let you punch logias. It sucks when it just make you immune to Law switching. The Ceasar/ Luffy fight was the sweet spot where it just let you interract with your opponent without taking away their abilities.
Bad guys don't "work around" abilities, good guys do. The immunity to Law's fruit is an explanation for why Oda can't write the most straightforward (aka most boring) avenue for his fights. It's how we got the Law/Kidd tag team instead.