However, we have to admit that the English pronunciation is not always perfectly taught to Russians.
I do not mean university courses and specialized schools. I mean the ordinary school education and some of the so-called "self-teaching books".

During my school education, I was never told that, for example, [ɪ] and [i:] (as in "fit" and "feet") are different vowels! As well as [ʊ] and [u:] ("pull" and "pool"). We were only taught that they were distinguished by their lengths. Everyone believed that you get "feet" if you drawl "fit" long. And it surprized me a lot when I learned that later.

And some textbooks I saw also explain that "fit" has a short "и" sound and "feet" has a long "и" sound, "pot" has a short "o" sound and "port" has a long "о" sound, "cut" has a short "a" sound and "cart" has a long "a" sound.

Many people I know who learned their English in school still believe in that "length-only" distinction.