Cattle farms aren't great for the environment, because cattle produces a lot of methane plus the production of food for cattle (since most don't just feed on grass on a meadow) that leads to cutting down of rain forests for soy plantations, etc. etc.
A feed additive made from red seaweed can reportedly reduce methane production of cattle by 80%. Development is underway by multiple companies.
Most faux leather is made from polyurethane or PVC, ultimately from petroleum; typically with a fabric backing, for strength. (petroleum will be around in smaller quantities for a LONG time, for chemical production, even when we no longer use it for fuel) The plastics are often subject to UV damage, and do not necessarily last longer in normal use than good quality real leather. I'll know how good Tesla's faux leather is five or ten years after I get my Cybertruck.

Moreover, leather is eventually biodegradable (although with treatments, that might take a long time in a landfill). Plastic really isn't, although it will eventually disintegrate into smaller particles, rather slowly if buried.
If the impact of livestock can be reduced, the natural products might be better for the environment.
I suppose if a faux leather were made from plant fiber plus biologically derived binders, dyes, surface treatments, etc, it might be the best alternative; but it could take decades to develop one that was as good for most purposes as the real thing, while having less downsides than the real thing. Of course, over millions of years, petroleum comes from biological sources too, but except for exotic microorganisms used in cleaning up spills, it's chemically different enough from its biological origins to have a whole different set of issues, for better or worse.