20 Mb/s is terrible. Sure, it'll work in some sense, but I'd go mad if that's the best I could get. A good wifi setup is way better than a cabled 20 Mb/s unless you absolutely need consist and better latency for some reason.
Doesn't a modern Wi-fi still has worse ping than CAT4 cable?
He said hard to reach places. If an old house has CAT4 in the basement, I'll take the lower pings, reliability, and at worst I'll WebDAV. Unless your home server is in the basement I can't see a normal realistic scenario where the data transfer isn't sufficient.