Ummm....they're both part of the skin. The only difference from real leather that is cut into squares is that it will originally have a very thick rough side that is peeled off if the application makes the thick part problematic, like with earpads. Otherwise for other applications like the leather slabs I use to hone my knives the rough side needs to be as thick as in the original craft leather cuts so they can take more of the polishing compound and then shave off as much of the burr on the edge as possible.
I personally prefer velour (it's hot AF down here) but you have to keep in mind that there are BIGGER problems in audio than the use of leather. The leather at least is made from livestock that also feeds people and pets, but what about the rest of the headphone? I'd hate to break it to you and others that share your sentiment, but there is no such thing as a totally vegan company if you actually take the animal suffering part seriously. Plastics are made from whale-murder petrochemicals, and before they get swallowed by whales, there were penguins and seagulls in that sludge. The metals and rare earth magnets used are mined with only some strong storm waiting to carry toxic sludge that will not just drown people but also displace wild animals (that are endangered, unlike livestock) even before the natural calamity happens. China has most of the rare earth mines, so not only are the mining ops a problem, but along with the headphone factories there, know that the money you spend eventually goes to some middle aged guy that refuses to use big pharma voodoo like Viagra and pays a premium for tiger and cobra testicles and rhino horns, plus maybe some elephant tusks for a statue on his desk.
Besides it's not like you can totally avoid the use of leather or causing animal suffering indirectly in your entire life. Do you get haircuts and get at least your sideburns shaved clean? if your barber uses a straight razor, guess what he sharpens that on. Yep, that's right, that leather strop hanging on his counter. You eat out? Sure the chef's knives might be made from old Jeep leaf springs and the handles made from recycled skateboards, but surprise, the chef might hone the knife on a leather strop mounted on a block of wood. Barber uses only electric clippers? Blades still mined and the housing is made out of whale-murdering petrochemicals. You eat bread, rice, and noodles? Tough luck kid, the farmland and dams needed to irrigate these are taking more and more living space from wildlife, and tigers, leopards, sun bears, and orangutans being wildlife are going to die out a lot faster than the cows you only see to be doing nothing but fart-punch the ozone layer but get all the love anyway (then again, cows are mostly vegan, unlike cats and primates that eat Bambi). How did you get to work today? Because even if you took a Leaf or a Tesla, they still roll on rubber, which is either farmed or synthesized, but doesn't biodegrade easily either way. It's like feeling good about not wearing leather like those animals in NYC Fashion Week that deserve to get paint all over their outfit but somehow forgetting where those Nikes are gonna go if they're too busted to go into a collectible sneaker collection.
Voluntarily getting a vasectomy and not having any children to reduce the number of humans that will need to use these resources can do more for the planet than worrying about livestock beyond outright abuse, like a city's worth of idiots abusing bulls in the name of tradition. Hell, taking care of your headphones and repairing them if possible is already one way to at least minimize the manufactured product going back to the earth as toxic waste. In other words, go enjoy leather if you want and use real leather that doesn't flake easily, there are more areas to make a small contribution than a product borne out of making use of every single part of the animal to minimize waste (BTW, collagen broth made from pork or beef bones can help with the joint pain from consuming too much tofu as long as you skim the fat).
