Discussion on answer by Серж: В русском языке есть дифтонги? Какова фонетика йотированных гласных по сравнению с дифтонгами?

Imported from a comment discussion on https://rus.stackexchange.com/questions/482442/%d0%92-%d1%80%d1%83%d1%81%d1%81%d0%ba%d0%be%d0%bc-%d1%8f%d0%b7%d1%8b%d0%ba%d0%b5-%d0%b5%d1%81%d1%82%d1%8c-%d0%b4%d0%b8%d1%84%d1%82%d0%be%d0%bd%d0%b3%d0%b8-%d0%9a%d0%b0%d0%ba%d0%be%d0%b2%d0%b0-%d1%84%d0%be%d0%bd%d0%b5%d1%82%d0%b8%d0%ba%d0%b0-%d0%b9%d0%be%d1%82%d0%b8%d1%80%d0%be%d0%b2%d0%b0%d0%bd%d0%bd%d1%8b%d1%85-%d0%b3%d0%bb%d0%b0%d1%81%d0%bd%d1%8b%d1%85-%d0%bf%d0%be-%d1%81%d1%80%d0%b0%d0%b2%d0%bd%d0%b5%d0%bd%d0%b8%d1%8e/482444#482444