I like this question, although I can't answer it.
I find one decent way if you've learned (or are learning) multiple languages is to compare them to each other.
For Spanish, I've never CEFR-tested it, but I'd estimate I'm at the C1/C2 level for speaking/writing, C2 listening, reading (at least for a Mexican-American Spanish blend...they'd drop somewhat for variations I'm less familiar with due to accent, etc). For French, I'd estimate B2/C1 speaking, C1/C2 listening, C2 reading, and B1/B2 writing with spell check). However, I don't really like putting CEFR letters to my French because I'm not nearly as sure of where things fall compared to with Spanish, where I have much more self-efficacy. It's much faster to think of what I can do in Spanish and refer back in French.
In French, I can follow the radio almost as well as I can in Spanish, I can read almost as quickly, but do come across more words per page that I don't know than in Spanish (where it's rare unless I'm reading a specialized topic). When speaking--which is pretty much just with my kids--I don't run into grammar roadblocks very often, but it does still happen much more than in Spanish, and it's more dramatic. For example, the other night, I wanted to say "tu pourras choisir un livre quand tu te seras brossée les dents"...I knew there was a way to construct the "when you have brushed" section, but couldn't figure it out on the fly and had to look it up later...I said it incorrectly at the time. Later I of course realized I could have said "apres s'etre brossée", which would have gotten rid of the need to know that tense. Similarly, I run into a lot more vocab roadblocks in French than in Spanish, because I simply haven't read nearly as much in French yet. I can write pretty much anything I can say in both languages, but my French writing is limited by my smaller vocab, shakier grammar, and much poorer spelling. So I can use the language with my kids and they're learning it very well, but I still become aware many times a day on French days of what I don't know yet. In Spanish, that's a lot rarer, besides some niggling grammatical doubts (e.g., "molestarlo" vs "molestarle") and the occasional word I don't know but reach for in a sentence (e.g., "horquilla", "vincha", and other things that have to do with my daughter's hair).
I'm not sure if that helped anyone, but to sum it up, instead of trying to objectively rate yourself, perhaps consider comparing your abilities to another L you have. I suppose this would work with your L1 too. I remember when learning Spanish, I noticed a big shift once I could speak fluidly due to building up enough grammar. It didn't matter that I didn't have all the words I wanted; the fact that when I looked them up, I'd know how to phrase them naturally made much, much, much more of a difference. I look forward to reaching that point in French; I still need more internalization of which verbs trigger the subjunctive, though, as well as when it's audible (e.g., "Je suis content que tu viennes aujourd'hui") vs inaudible (e.g., "Je suis content que tu m'ecoute"). Oh, and things like the de/du/d' partitive, and how the future tense is used in situations where you'd just use the present tense in Spanish, and...it goes on.