The point wasn't to pedantically count diphthongs, it's the idea that English is biased towards them in a way that Germanic languages aren't, and which affects

The point wasn't to pedantically count diphthongs, it's the idea that English is biased towards them in a way that Germanic languages aren't, and which affects their pronouncation if left uncorrected. If it helps, replace "most" with "many". This all depends on dialect, of course. Words like "ride" can occur both as diphthong (/ɹaɪd/) and monophthong (/ɹa:d/). Southern American dialects have things like vowel breaking that further puts a spin on vowels.