Yeah. I can see that. Let me see if I can expand.
1. Keigo falls into the category of “specific purpose” (SP) language. SP language can be relatively simple things like tourism language, or it can be very deep and technical like scientific, medical, engineering, etc. SP language is typically taught and learned on a need to know basis, and it’s totally possible to be highly fluent (usually measured in terms of general proficiency) and not know anything about SP language.
2. Keigo (and this is way more than basic formal and honorific language) is used in very specific situations. As a foreigner, in almost all cases that matter, there will be an interpreter or the foreigner will be trained in keigo.
3. For reference, I think that most of the keigo that I would recommend a non-native speaker learn can be found at this link (it’s a small and easy to learn list):
https://www.fluentu.com/blog/japanese/japanese-keigo/
Furthermore, I think that most of this language is more useful receptively (listening and reading) and will almost never need to be produced (spoken or written).
4. As far as proficiency goes, most keigo would be ILR 5 / CEFR C2, with the basics linked above being ILR 4 / CEFR C1 (used dynamically… much lower as memorized set phrases). When you’re at that level and needing keigo, you know you are lacking in keigo and make an effort to learn it. Before that would probably be a learning sequencing error (other than nerdy curiosity).
Beyond learning the content in the link above, most foreigners will not find themselves in the context of needing to know or use keigo. As special purpose language, it should really only be pursued if necessary. Otherwise, the knowledge learned will most likely be forgotten due to lack of use, or it will be used awkwardly and possibly inappropriately (as I mentioned before).
If it’s just a nerd itch to scratch, then go for it. For most people, I think there are more compelling aspects of Japanese to spend time on.