Use of wasn't vs was not in a formal sentence

In the following sentence :

The figure was tall, bespectacled, although in spite of the opacity of the glasses it wasn’t immediately clear whether or not he truly was blind.

I am told the use of "wasn’t" is insufficiently formal enough in comparison to the rest of the sentence, and that I should use "was not" instead.

Would the sentence be shocking/uncomfortable to native-readers?