Hi Biglou....... good to see you over here from the CAD forums.
You are discovering one of the "rules" (all rules can be broken by a Chajin) for chawan that many non-tea studying potters do not "get". Yeah.... rough interiors are not so good for chasen.
If a tea practitioner is using a GOOD chasen ($$$) not good at ALL.
A lot of the "gnarly" chawan you see in photos are certainly visually dramatic and very beautiful, but for actual matcha use and certainly for actual formal Chanoyu use........ not very useful.
At an invitational international chawan exhibition I was involved in a number of years ago I invited an Ursenke master to come to the exhibition. She said she really enjoyed the internesting chawan there.... lots of differnt approaches and ideas..... but said that most of them could not be used for Tea (capital intended). Roughness/harshness of a number of areas of the forms was one of the prime culprits.
While many of my chawan are rough looking on the exterior, great attention is paid to the surface and contours of the interiors. (Just one of the reasons that the failure rate for my pieces "making the cut" is so high.)
There is a reason that in Japan certain types of wares are tended to be favored for chawan and chaire (tea caddies), and others are favored for other ceremony objects. Shigaraki yaki is not usually known as a major choice for chawan....... but is for stuff like hanaire and mizusashi.
I save the really "nasty" clays for mizusashi (fresh water jars), hanaire (flower vases), and sometimes stuff like futaoki (lid rests). I save the really "crusty" firing locations for the same. Often Chawan are put into saggars or behind "shields" that keep them from getting too much rough ash accumulation. Sometimes Chawan are fired upside-down.
As Paul has said, the wet/dry paper is in constant use for woodfirers. Also diamond grinding wheels of various sorts.
Yes, there is "bowl contact" when whisking, for sure. You are not "bearing down" hard, but you need to make sure that ALL of the matcha is getting blended into the water. Nothing worse than some dry matcha hitting your mouth!
For ceremony use, the host does not want a bowl that he/she has to be very careful in using so as not to break tines (and potentially kill the guest). Part of the nature of the ceremony is that it be very natural and effortless looking (even though that is FAR from the case until you've practiced it for 60 years). So "concentrating" on avoiding a chawan's "issues" is not a helpful thing.
However, some might say that having to deal with a bowls "imperfections" focuses the attention... and forces the host to be fully "in the moment" as the tea is prepared. Zen. I'd think most "mortals" at Tea would save this challenge to late in their development
For "home use" you are into the ATW department. (A