As
@pvamax said, you can't go WOT from a standstill, it's just how it's designed.
The way a jet pump works is not just only by shooting out jets of water backwards, but also by the intake pulling the boat forward as it sucks in water. If you could aim the jet nozzle straight up, the boat would still move forward from pulling water in.
That said, the impellers and engine are setup together so that the engine can spin the impeller to generate enough thrust so that the engine is right at the Rev limiter. If the impeller isn't aggressively pitched, engine is at the rev limiter, but not doing that much work and wasting energy, and not going past the rev limiter as to not damage the engine. Too aggressive of a pitch (this is when, I think, you won't have cavitation issues) because the resistance to force that much water out would prevent the engine from hitting the rev limiter. It's a balancing game.
I have a 2012 Challenger 210 with 430hp, thanks to superchargers. With just me on the boat, I can go from a standstill to WOT with minor cavitation. If I do the same with 6+ ppl, I will experience cavitation as there's more weight on the boat (more resistance), requiring more thrust to push, with impellers having to spin faster to generate. The reason for me to cavitate, and why I mentioned earlier about pulling in water, is because if I immediate tell the engines to spin that fast to get enough thrust, it will easily. But the added weight makes it harder for the boat to initially move forward to provide enough water to process. What is actually happening is, on the intake side, you're creating a massive low pressure zone, causing the water that can enter the intake to boil or vaporize. This leads to less dense water being processed (as its aerated), and not a lot of thrust, which makes going forward harder than if you progressively applied the throttle. And as the water is less dense, impellers aren't getting much resistance compared to denser water and able to hit the rev limiter quicker, which is not good. For me, with superchargers, the engines will try to go past the rev limiter, spinning the SC, but once I "hook up", i think it engages the SC at bit rougher as the SC has to disengage to slow down when it tries to go past the rev limiter, that when I do hook up, its essentially dumping the clutch in a car and not good.
Best way to understand what's happening is to think of it like a car on ice. You need to apply enough power to the wheels, in a slow fashion, to maintain traction between the wheels and ice. The heavier you are, like a semi, the slower you need to go as you need more traction to get you going from a stand still. If you're a small golf cart, it's so light you're tires can make enough traction that it's not a big deal. BUT, if you slam on the gas, you'll spin the tires. Sure, you may go forward but it'll be slow and not as fast as if you just slowly applied power. Our boat's do the same thing. With jet engines that rev as high as we do, getting traction is important. Even if you don't have a SC, still probably not a good idea to go WOT from a standstill if you're caveating as you say you do.
Sorry for the long message, but hopefully if you or anyone has questions or concerns about it, at least understanding the fundamentals as to why it's happening, can help ease some worries.
