I think you're dead right, Screamer, when you point out how important the gusts and lulls are.
Whether 8kg is worth "X" width or "Y" length is something it would take one hell of a lot of testing to find out, and in the end it would depend on the wind strength, sailor, gust/lull structure etc like you say.
I used to love slalom racing and did it to world title level, but never liked it in marginal stuff, when I preferred a powered-up longboard. Some other guys love getting onto short boards as early as possible. As you say, it's a personal thing and to each, their own.
Unregistered; in places like Germany, Holland and (to a lesser extent) the USA, Finns are quite popular. The German Finn association has half as many members as the entire German windsurfing association. Are you telling us that all those old guys sailing Masters divisions in Finns are trophy hunters? With 550 members in Germany and Holland alone (compare that to most windsurfer racing classes) there's no way the class is dead (and I'm not even a Finn fan, but truth demands that we look at reality rather than pretending we know it all).
Interestingly, one of the Finn's big rivals is the O-Jolle, which is like an even heavier and older Finn which is still very popular despite getting very little publicity. These guys aren't trophy hunters and their boats are not dinosaurs - in fact they are much more popular than Musto Skiffs or foiler Moths.