Just in case you didn't know, an OEM stock car with only a tire/wheel change won in M2 at the National Championship. Yes, other than wheels and tires, a OEM stock car managed to beat "full rally cars." And guess what, that same car finished 2nd in PF.
I'd argue that rule 6.2.4a would allow your car to compete in the Stock class. There is a school of thought in the RallyCross program that stock means OEM stock. Does your car have a "trunk kit"? If so, those parts might take you out of stock as well.
If you don't like the rules, get involved with the rallycross program and get them changed. Create some wording that road race vehicles are eligible for their equivalent RallyCross class. As a starter, here's the rule that applies to SS vehicles taken from Section 13.0 and on page 70 of the Solo rule book:
Cars listed as eligible in and prepared to the current national Showroom Stock Club Racing rules are permitted to compete in their respective Solo Stock Classes. This does not include Showroom Stock cars with installations of post-factory “performance packages” otherwise known as “trunk kits.”
RallyCross is made up of regular folks like you and me that want to have fun. Maybe the original rule makers didn't think that a road racing car would be interested in running a rallycross. Have you noticed how "thick" the RallyCross rulebook is? If some rules keep you from wanting to experience the fun, well maybe rallycross is not for you.