I will answer you with examples in English: does the vowels in English help us reading?
Probably yes, but one still should distinguish between the "oo" of "look" and of "door",
and between the o of "more" and of "move"..
In the same way, letters like א ה ו י supply us some hints according to their place in the word, but it is far away from 100% guarantee..
So in order to be fair, the vowels in English are doing 90% of the job;
while the letters אהוי are doing just 50% of it..