German tree versus other trees
Why is German tree twice as big as the Italian tree or others? Does that mean the proficiency level in German, compared to other languages, is higher after completing the tree? Over 120 circles in German course versus 62 circles in Italian or Spanish...
The German tree may have twice as many skills but those skills are less populated than the Italian or Spanish ones. If you look at the number of lessons you can see especially German and Italian being fairly close to each other. (That post is old but the numbers seem accurate). Of course, we can still have the same conversation about Norwegian and Turkish based on that data.
"Why is German tree twice as big as the Italian tree or others?"
It's actually smaller in terms of total lessons than the Norwegian tree- it just splits fewer lessons into more skills.
The German tree has received some tree updates in the past, I think we are currently on Tree 4.0 or 4.1, because of the small revision. Yes, your proficiency could be a bit higher.
You can sort of see the history of the German tree here: https://incubator.duolingo.com/courses/de/en/status
It is SO daunting though, isn't it? I had a trophy once for completing it, but then they added like 20 new lessons and I've never been able to snatch it back again.