Gotcha. Yes, if you have your cache (let alone services) all across different machines, then this is all irrelevant.

The real question, which few ever ask, is whether your app actually needs more than one server. Servers are so insanely large (up to like 400 Cores) and powerful now that you can get meaningful scale on a single box.

If you can colocate the app and cache (and maybe also the db) on the same server, you can get many orders of magnitude better performance, regardless of which cache it is. Redis, memcached etc all can do 100k or more gets per second (dragonflydb etc claim 10x that due to multithreading).

Hell, with RAM being so expensive now and NVME so fast, sqlite is a VERY attractive option for cache. Plenty written about projects adopting it. Rails in particular is a champion of it.