Right now, you're right that paragraph (a) has basically the same wording as we currently have for the current hate crime mischief offence, which uses the words “primarily used for religious worship”. My guess would be that in crafting paragraphs (b), (c), and (d), the drafters of this bill decided to use the same terminology for the remaining parts; thus in paragraph (b), for example, it would be a building that is primarily used as an educational institution—for example, a university or a community college.
If one were to take “primarily” out and just say “that is used”, then it broadens the scope considerably, because it really wouldn't matter what the primary use of the building was; it would matter more what it was being used for at the time, presumably, that the mischief took place.
It's the same with the other paragraphs as well. Removing the term “primarily” and just using the term “used” would be definitely an expansion of the kinds of buildings that would be protected by the bill.