Putting servers with different views of the DNS in resolv.conf seems unreliable to me, even with glibc's behavior. If the first server "glitches" for any reason

Putting servers with different views of the DNS in resolv.conf seems unreliable to me, even with glibc's behavior. If the first server "glitches" for any reason, the process will get the response from the second server, which might not be what you wanted. And worse, some processes (like browsers) have their own cache of DNS responses, so the incorrect response might get cached. That is: it was already broken, systemd-resolvd just made the breakage more visible. (If I understood it correctly, it only switches after the first "glitch", so the only difference is that it doesn't switch back until the second server also "glitches".)