One of the problems in english (not the only one, but one of them) is that for the vowels there are 5 graphs (is this term correct? Sorry but hope it is understandable) but many more sounds. In Spanish there are 5 vowels in the latin alphabet and exactly five sounds and nothing else.
Valencian has 7 sounds though, two for e and two for o. Similarly, Catalan also (and in some circumstances the o sounds as u, when the stress is not in it and other stuff). But they still have quite strict rules.
Yeah but we represent a lot of vowel sounds by combining vowels - 5 letters (not including y), if we allow any combo of two to represent a different sound that's 25 combos, and if we remember that preceding and following consonants can modify vowels too (though, dough, caught bought vs thou, bao, sour, or; on, con, Ron vs how, cow, ow) that's quite a lot of combos.
Now, you can (and should!) accuse me of cherry-picking examples, since the rules are less consistent and/or vastly more complicated than what I represented. But I maintain that there are orders of magnitude more ways to represent vowel sounds than 5, and the clue is the context. Not, as many will suggest, memorizing each individual case (though there's certainly plenty of that going around, much like Spanish's infamous irregularly verb conjugations), but understanding categories and families and patterns.
English sounds usually are best understood with groups of three letters, rather than one letter at a time. If you looks at throuples, you'll likely find far more of that consistency we all so deeply desire.
Yes, English is VERY consistent. The problem is that there are multiple systems working inside English vocabulary, so you have to get familiar with more than one rule set.
Valencian has 7 sounds though, two for e and two for o. Similarly, Catalan also (and in some circumstances the o sounds as u, when the stress is not in it and other stuff). But they still have quite strict rules.