Do you really think that the "pros" determine what classes die?
There's a small handful of pros out there compared to the millions of local regular racers. We the local racers determine which classes thrive or die.
I can tell you for a fact what killed 10th nitro truck. Myself, Robert J. and Efren actually lived and raced during the peak of nitro truck. This was in the mid to late 90"s.
What killed the class was the 1/8th scale nitro classes. Everyone stopped racing nitro stadium truck and moved into the 1/8th scale stuff.
Monster trucks were never a racing type of vehicle and local tracks made classes to accomodate people with those trucks.
Classes come and go all the time. It's the local racers that determines what is popular at their local tracks.
Pros don't even like the short bus class, but they race it because the local racers made it the most popular class and when they win on Sunday they sell kits on Monday, period.
I've driven every brand out there and I choose to drive Kyosho because I feel they offer the best quality kits, not because Tebow drives them.
My advice is to pick a quality brand and stick with it. Don't jump around to different brands because you think it's the latest greatest. Practice as much as you can and learn how the different changes effect your vehicles.