Les has raced his XR75+ succesfully at National level. There are other examples as well.
Conventional wisdom and painful personal experience has that a half litre 2 stroke MXer is much more dangerous than a close to the ground, light and low powered mini.
At the VCM Yarram round last year the first 5 or 6 of the modern 85 cc minis running as supports, were clearing the 50 or so foot tabletop. I saw one classic bike out of about 60, an RM370 piloted by a young A grader, clear it a couple of times.