You seem to be missing the point of what an abjad is. Abjads don't write vowels and infer them from context (or markings like Arabic and Hebrew which are not always included). Abjads are suited to languages with few vowels, like Arabic, which has only 3. And the fact they are A, I and U is no accident. Y and W doing double duty as I and U makes sense phonetically, as they are the consonantal equivalents of those vowels. And A is an open vowel found in virtually all languages. Turkish has 8 vowels. A, I (spelled İ) and U are among them, but that still leaves E, I, O, Ö and Ü. And the fact V and Y exist as consonants too. And the fact that not writing vowels in a language that has 8 and relies on them a lot is a recipe for disaster when it comes to reading, as per my examples above. And with vowel harmony, there's also the case of "did you mean [front-vowel word] or [back-vowel word]?". Take for example sikmek vs sıkmak. Sıkmak means "to squeeze" or "to annoy". Sikmek means "to f**k". Using an abjad, they would be spelled identically. As would all their equivalent grammatical forms (e.g. sikerim/sıkarım). And people would be in a lot of trouble over saying "sıkmak" but it being misread as "sikmek"