Of the European languages, French is next hardest for learning to spell, after English which beats all others, but English beats French by several thousand words with unpredictable letters.
Learning to read French is almost incomparably easier than English, and especially for foreigners. Quite a few French sounds have different spellings (e.g. the English long oo sound in 'ou nous tout choux') but the pronunciation of French spellings is regular, with only minor problems like a final consonant being silent before words starting with a consonant (tout que), but pronounced before vowels (tout a).
So children don?t need to be taken through wordlists like Mrz?s
look, book, took, cook, good, hood, brook, stood, crook, wool,
room, broom, moon, pool, cool, spoon, balloon, groom, stool, roof etc.
for learning to read.
The sound of French ou does not constantly vary as in
sound soup shoulder should double....
Such phonic inconsistencies are the reason why learning to read English takes children much longer than other European languages (as Seymour et established in 2003).
I'm sure even Mrz is able to see that if ou always had the sound of 'shout out loud', learning to read words with that grapheme would be easier.
Coming back to letter names and sounds of the OP,
the vowels a, e, i, o and u
have the sound of their name as often the first sound which children are usually taught for them (able, even, island, only, use).