I think most people going out their way to pay for an alternative Reddit client have a beef with Reddit in the first place, and it's the client that keeps them on the platform.
Would they be happy with Reddit alternatives ? who knows. But they'd probably give a fair shake at it to see if it fits their needs, and not just dismiss it at first glance. Also would such a service be profitable ? depends if service such a minuscule group is done efficiently enough to keep the running costs low.
IMO Apollo users probably aren't on Reddit for the mainstream stuff, Mastodon or Bluesky could probably take that role. Niche communities could probably move on to smaller services and their users would follow.
PS: Voat was positively horrible, but I'd argue the circumstances that led to its conception where wildly different. This time we hopefully wouldn't have some "free speach" narrative baked into it, except for the NSFW bits perhaps.