I'm sorry that you had such a bad experience, there's really no excuse for an outfitter to not check and make sure a canoe is balanced, esp at $30/day.

The only thing I can think of that would make the boats into slugs would be if the bow seats were stuck all the way forward, not allowing you to trim the canoe. A heavy bow would probably eat the glide. At 18.5 feet long the MNII should seem skinny and shallow the first time you get in it (from the stern position), small despite its length.

If you depart on your next trip through Ely you can borrow my "so ugly it should be slow" MNII, you might still be frustrated but at least it will be free.