Yes they seem too big. I already mentioned this once before in a special topic I made for this.(Got no reply) I even made special holder for 7mm nuts so I didn’t have to reprint nearly every part. :p I really don’t understand more people have this problem, but it’s easy to fix with the parametric version in your case.
If i open the parts in Netfabb the slot are 8mm. (Which should be 7mm) So yeah as I said, a bit annoying, but not a real problem for an otherwise great design.