> is trivially provable that Cyrillic script is better adapted even to languages which do not use it today, but have to resort to digraphs or glyphs with diacritics
Take a look at the Cyrillic section of Unicode to see your trivially provable claim being trivially disproven. You'll see all the same digraphs, glyphs, accents, graves etc. as used in Latin scripts.
It's also easy to see it easily disproven if you look at all the languages USSR forced cyrillic alphabet on.
Most of the extra glyphs are for non-Slavic (Turk languages of Central Asia and Siberia). You see the same (and worse) in Latin Unicode pages — just look at how many variations of vowels 'a', 'i', or 'e' you have, consonants like 'c', 'z', 's'…
To be fair, the parent post was clearly talking about Slavic languages, not "all the languages USSR forced cyrillic alphabet on", which were not Slavic and which required significant modifications to the alphabet.