As it stands Roon will only override Roon-supplied with user-supplied lyrics when they are of the same type: synchronized with synchronized and unsynched with unsynched. In particular, trying to override Roon-supplied synchronized lyrics with user-supplied unsynched lyrics does not work.
As anyone who’s ever tried to generate synchronized lyrics can tell you, it’s a pain. Even @Rugby, in his unofficial guide to using the lyrics tag in Roon (1.7 Lyrics Tag Guide) confesses that he tried 3 times to get his example completely right, ran out of patience, and gave up.
Please change Roon so that it overrides any Roon-supplied lyrics with user-supplied lyrics whenever the latter are available and regardless of whether the the user-supplied lyrics are synchronized or unsynchronized.
This problem is worse than what you describe. The Roon supplied lyrics can be more than just wrong. The lyrics can be someone’s bad idea of a joke. For example, someone added insipid rock lyrics to a Bartok orchestral piece that should not have any lyrics (Music for Strings, Percussion & Celeste, Sz. 106, BB 114 - Andante Tranquillo, Fritz Reiner, Chicago Symphony Orchestra). Why isn’t there a way of just indicating that the piece cannot have lyrics?