The brown fleet was a money pit as well but for the providers of the sails (I believe these days mostly Gaastra but possibly others, Gaastra was going more and more in the direction of sports goods) it was still a money maker.
The key here is that Dokman was amazingly knowledgeable through his long term interaction with the people running the brown fleet vessels, who - as you pointed out - also love to have an edge in their races and TD sails were amongst the best there were at the time: absolutely legal with respect to techniques and materials used but meanwhile engineered with the best software that we could lay our hands on or build ourselves.
So you could be a recreational or for-hire vessel on most days and a potential race winner if you decided to enter a contest, and they looked spectacularly clean. That gave us the best of both worlds, a step-up into high tech while still mostly using traditional materials and techniques.
Edit: Theo died a while ago and I still see TD sails every now and then and it always reminds me of a great time. I didn't have a house back then (housing shortage in NL is not something recent) and slept above the sailmakery :)
Here are some in their natural environment:
https://primary.jwwb.nl/public/p/r/h/temp-wqhdccofnxpbaxjxoo...
(not the traditional 'sword' visible on the side, a large wooden structure on a hinge that could be lowered for stability, these vessels are extremely shallow because they're made for inland waters and shallow 'Waddenzee', the typical draft is less than a meter).
More of the same vessel:
