Actually, Welsh is far more phonetic than English ... it’s just that Welsh letters have a very different sound than letters in English, so it seems weird to us. The C always sounds like an English K (even when followed by E, I or Y), the F sounds like an English V (it is the Welsh FF that sounds like an English F), the Welsh TH (which is considered one letter) always sounds like the TH in “then” or “than” (the initial consonant sound in “the” and “this” and “that” is spelled with a DD (also considered one letter) in Welsh), the Welsh W can be used as a consonant that has two possible sounds, exactly like the English OO (sometimes as in “took” and sometimes as in “tooth”), etc. Fascinating language.
Oops, I see that you already had made many of the same points that I made. Esgusodwch fi. : )