Sure, there are some cases where O() can be misleading, but those are the exceptions. You can work in software for a long time without being affected significantly by them, whereas using O(n^2) when you could use O(n) can make your code 1,000 times slower than usable, and it does this frequently.

I have fixed hundreds of O(n^2) algorithms over the years, made them O(n) or O(n log(n)), and made the product dramatically better. The fact that an O(n) algorithm can sometimes be slower than an O(n^2) feels more like pedantry than useful information in this context.