A few things to note:
Feld didn't get rid of the World Finals on Pay Per View. Monster Jam stopped that after World Finals 3, probably because it wasn't making enough money, or other business reasons.
Also, I know what you mean when you complain about multiples of the same truck at the World Finals. Grave Digger definitely has a monopoly on the sport when it comes to who is on top for the most part, so it's kinda boring seeing that many Diggers at one show. That being said, it's not about the trucks that are there, but the drivers who get there. I can't speak for the drivers, whether getting to the World Finals is more important than just going out and putting on a good show for the fans, but it would make trying to win seem a bit pointless if you're systematically never going to make it to the Finals as a part of a team. Overall, it's more fair to the drivers themselves, rather than the amount of different trucks who make it there.
I do agree with you about the World Finals track being uninspired and cluttered. They did a much better job last year, but from 2014-16, it was just two giant islands of dirt that seemed to have no breathing room or sense of strategy. I don't think the tracks should be too challenging or designed to be absurd (ie. World Finals 11), but sort of the best of all the jumps from that season with enough room to maneuver. World Finals 12 is a great example. I strongly believe that most of the 2000's tracks wouldn't stand a chance to today's trucks, but they could certainly make things stand out more and use some inspiration in the paint. It was nice seeing them start using more cars in the jumps this year, but it pretty pointless, considering they were just there for structural integrity, something that dirt does a better job at. They should have cars that are there to be crushed on top of the dirt piles/ramps, but not to where the jump itself is useless once they're crushed. Overall, people still want to see things get destroyed.
All that being said, you're still too pessimistic.