"Most people don't have the skills to design and build competitive boats these days. Just handling pre-preg carbon is quite laboursome. An autoclave is out of the question for most garage builders, as is the math for lay-up schemes and foam/glass composite panels."

I agree that the techniques you mention are not for garage designers but,

1) These techniques are for volume builders, there are other techniques that yield very similar results that are suitable for the garage builder

2) The 18HT is not cutting edge in terms of weight and materials. A platform weight of 120 kg is feasible using wood epoxy carbon, aluminum beams, and carbon mast. If you used synthetic rigging you might be able to use an aluminum mast.

3) You could probably modify a 5.5 uni or Inter 18 to come close. If you did, you would end up lighter aloft than a purpose built 18HT.

Yes, a garage designer could compete in 18HT

As a side issue, one day this winter put all your Tornado's standing rigging in a pile and weigh it, I did, it shocked me