Here is an interesting discovery about the old percentage rating, which is now gone.
I am not endorsing the new system at all, I hate it, but I wanted to add a bit of perspective. I have been reading a lot of posts from people who's German level is at 25 and yet they say according to their percentage on the old system they were at 65% or better. I am only at level 16 or so, but my percentage rating was at 62-63. I studied German in country in Switzerland, almost a kind of oxymoron if you know Switzerland. Anyway the percentage rating was a false flag.
I never put much stock into it based on reaching 25% without even completing level 2.
Yeah, I sincerely doubt that Duo gets people to a 60% fluency level in German anyways. Duo seems more for getting your foot into the door when learning a language. After you are done with Duo you will find that there is still a lot of work to be done. I never liked the "fluency" thing. It never made sense.
I never really saw why the fluency percentage was so bad, I think it was fairly accurate. I think the main issue was that people got confused when they couldn't get to a hundred percent.