There are any number of reasons a user might want to override Roon-supplied lyrics. Sometimes Roon’s lyrics are just wrong (e.g. Roon's synchronized lyrics are wrong. How can I fix them (without undue suffering)? - #7 by BlackJack), sometimes Roon supplies only foreign language lyrics without translations, sometimes Roon supplies translated lyrics that are superfluous (e.g for Kraftwerk), etc.
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.