I think it's good to encourage gifters to use their giftees wishlist, but I also think it should be ok to deviate a bit. I like the idea of getting at least one item off the wishlist and then the gifter could choose to get other items off the wishlist or go a little outside of the box.
I think if people want others to strictly go off the wishlist, then the giftees need to make sure they have an accessible wishlist. One year it was hard for me because my giftee pretty much just wanted promo items and rare amiibo and that can be tricky to 1) track down and 2) stay within budget. Part of the fun for me is the hunting down items locally, if I'm required to go on eBay, that's just not as fun.
Personally, as long as I don't get a duplicate, I'm happy to be surprised. An alternative system could be having the giftee just communicate through their wishlist and either say- please stick to my wishlist so they are not disappointed, or say hey I like surprises, based on my collection, what do you think I would like/ I am missing? That way everyone is happy.