What's the exact realization of Chinese glides (in medial position)?
The distinction between [pʲu] пю and [pju] пью for a Russian speaker may be very salient, but for the majority of Mandarin learners of Russian, it is a very difficult one to pick up.
That is because the equivalent phonetic difference is not phonemic in Mandarin, and it does not matter much for comprehensible Mandarin. It is thus unsurprising that the glide is more audible in slow Mandarin than faster-paced Mandarin.
Nonetheless, acoustic analysis from several sources as well as psycholinguistic tests e.g. involving rhyming and game languages seem to all agree that in Modern Standard Mandarin, the glide is part of the onset.
Note that diachronically, the glides of Middle Chinese were firmly in the final, not the onset, and this is still the case for many other varieties in Chinese, e.g. in Taiwanese Hokkien.