Vehicles do not ruin FPS games, sorry. Halo is still great, pretty much forever because of vehicles. And so is GTA.
Now, vehicles done badly, yeah that sucks for everyone.
Two ways vehicles could be bad. One is they just sook, like they don't feel like vehicles, slide sideways, have physics which are trash. They can also suck by not being worth it or being too op or whatever. The second way they could suck is just not being theme oriented. That second one is going to be hard to do in Apex. It's clear there are vehicles, there are trucks and tractors everywhere. In the titanfall universe, vehicles abound.
But adding vehicles that are combustion engine could just scream of dumb. Apex is on the low tech end of a high tech universe. I mean wraith and Loba basically use limited teleportation. There are freaking gravity plumes. And you have other themes like dropping with just a rocket pack from the sky, etc. etc....the vehicles are going to kind of have to fit with the idea of the game.
I really don't know how it's done to make it all work. It would take a lot of thought, but could be great. Obviously, it's got to be about the transportation here...things like minigun Warthogs and tanks are not going to be good for Legends. I'd keep it to small cars, and motorcycle things. Oh, and fuel is doomb. Fortnite vehicles would be fine if not for the ridiculous fuel rules they use.
I'm not opposed to vehicles, but like anything else, done well will be fantastic, done poorly will ruin the whole bag.