In the CEFR, levels C1 and C2 are not about how much grammar you know but about the range of linguistic skills you have. Below are the "can ..." statements for level C2 in the Common European Framework of Reference (CEFR) self-assessment grid
- Listening: I have no difficulty in understanding any kind of spoken language, whether live or broadcast, even when delivered at fast native speed, provided I have some time to get familiar with the accent.
- Reading: I can read with ease virtually all forms of the written language, including abstract, structurally or linguistically complex texts such as manuals, specialised articles and literary works.
- I can take part effortlessly in any conversation or discussion and have a good familiarity with idiomatic expressions and colloquialisms. I can express myself fluently and convey finer shades of meaning precisely. If I do have a problem I can backtrack and restructure around the difficulty so smoothly that other people are hardly aware of it.
- I can present a clear, smoothly-flowing description or argument in a style appropriate to the context and with an effective logical structure which helps the recipient to notice and remember significant points.
- Writing: I can write clear, smoothly-flowing text in an appropriate style. I can write complex letters, reports or articles which present a case with an effective logical structure which helps the recipient to notice and remember significant points. I can write summaries and reviews of professional or literary works.
This goes far beyond levels B1 and B2, but does not mention any specific grammatical structures, even in the more detailed CEFR documents, because the descriptions are intended to be language-neutral.
However, if you want to read and write German at level C2, i.e. "read with ease virtually all forms of the written language" and " write complex letters, reports or articles", you also need to master grammar that is not used in 99% of normal speech. To take the specific example of konsekutive Konnektoren, these are essential at levels C1 and C2 because you need to be able to write coherent texts rather than simply stringing sentences together. You can develop very good writing skills without ever using Partizipialsätze, but if you want to be able to read "virtually all forms of the written language", you need to understand them.
C2 used to be described as close to native, but this was abandoned in updates of the CEFR. (Even native speakers vary considerably in language skills.)