Would such a masoretic text of Isaiah contain vowel markings? The masoretic text of the Pentateuch should, as it was recited aloud in a formal setting. But why would Isaiah contain vowel markings?
You tell me? Are vowel markings essential to the accurate transmission of the text - or mearly an adaptation to assist the translation because of separation from the language caused in part to the diaspora?
DSS Isaiah contains similar vowel marks. Quram scribes added some semi-vowels to the text, mostly the use of yod, waw, and “he”.
Since the written hebrew is comprised of consonants, some means throughout the written history some means of informing the reader what vowels to use had to be devised.
Bottom line is vowel markings mean little to the translation - just a aid for translation.