The problem with language learning "levels"

Most language systems and books have different levels: Basic, Beginner, Intermediate, Advanced, and so on.

I don't really believe in levels very much, because my experience is that people take very different paths to learn a language. One person might speak English like crazy after a few weeks but make tons of grammatical errors. Another person might know a lot of academic vocabulary but have trouble understanding casual spoken English. Someone else might have good pronunciation and listening comprehension, but not be able to read. Trying to fit each of these cases into a "level" system is pointless.

It's also hard to split lessons up into different levels. For example, look at a sentence like this:

I just thought I'd come out and get some fresh air and sunshine.

What level is this sentence? In some ways, it's really simple. You can easily remember the phrase "I just thought I'd..." and replace "come out" with some other action:

I just thought I'd watch a movie.

I just thought I'd go swimming.

But even though it's pretty simple, I would guess that most English learners probably don't use this expression. Even those who think of themselves as "advanced" learners probably don't know about the phrase "I just thought I'd..." because it's not something that's taught in schools or books.

It's easy to measure the level of something that grows in a straight line. Some language-learning courses give you the idea that language ability can be measured that way. But I don't think that's true. That's why I hesitate to break PhraseMix lessons up into levels.

What do you think about that? Am I making it harder for people to learn? Or do you agree that levels are not necessary? Let me know in the comments!