You would probably just sound like a non-native speaker. I assume it would be similar to weak forms and how weak forms are usually absent from non-native english speech.
As a non-native speaker, I was kinda confused at first by this comic because in my head the vowels definitely didn't sound all the same. But I personally consider pronunciation of vowels in English to be one of the greatest mysteries in the universe, so no wonder.
As a native English speaker and Spanish learner, consistent vowel pronunciation is so incredible. 🥺 Just looking at a word and knowing how to pronounce it… amazing stuff. Kind of wild that in some languages you don’t have the ‘curse of the self educated’ (randomly mispronouncing words you’ve only read, not heard spoken).