Sorry but this sounds like nonsense. Vowel distinctions absolutely matter in English. Think of how many words would be indistinguishable otherwise: bout, bought, bet, bat, bit, beet, boot, boat, bite, but, and bait are all distinguished from each other only by a vowel.
(And, yes, these all sound quite different to me, an American, though non-native speakers often have trouble making or recognizing some of the distinctions. Some native speakers further distinguish “bot” from “bought”, but I don’t.)