I have a .50cal flint rifle I built using a GreenMtn 7/8 a/f bbl. I use store bought .490 RB. I use heavy denim cloth for patch material and it requires a short&long starter.
With the same load that I generally use at the range of 65gr FFg, the rifle will group better with a 50cal over powder wad (1/8") than w/o. Not by a lot,,but it's very noticable especially at 100m.

I had these wads along with filler and overshot wads all in 50 cal for another M/L smoothbore long since gone down the road. I thought I'd give them a try in the RB rifle a couple times out in different combinations and loads starting 2 summers ago and the Ov/Powder wad got good results.
These wads aren't particularly tight fitting in the rifle, they do fit & slide squarely and easily down the bbl. So I doubt they play much if any bore seal role.

Does it prove anything?,,No not really other that in one case (this one) for some reason the rifle liked the combination. It may balk at them if I changed ball dia, patch material or patch lube (1:1 crisco & T/C Bore Butter) or switched powder type,,ect.

For now, I like it, it works good. It wasn't meant to clean the bore as the lube and tight patch I use allows 30 or more shots before I clean the bbl. No crud ring down in there even at that many shots but I feel I owe it to 'her at that point.