Well, i m not an engine guru by fahr lol, but there is some things that is kind of missleading or not quite related to what you compare things to :-)

Like:
Boats, their high RPM is abaout 23-25000rpms for 3,5ccm and thats a little higher than an onroad clutch engages, so you can not really compare.

onroad enignes use conical manifolds, and that also offsets things a bit.

I have very little knowledge abaout this but i have been explaind by some books and a coupple of well educated people.

When it comes to two strokes +exhaust systems and tunedpies/manifolds, alot of the buisness is abaout time - like in milliseconds.

F eks: at 30.000 rpm, exhaustport is open at y time in ms. If the charge of fresh gasses need 2.5 ms to reach back into the combustionchamber and the pipe/manifold is set up to use 5 ms then you will need a shorter manifold to achive the desired power or torque output. If you exhaust is set up to only use 1.5 ms, then you will need a longer manifold.


Ofcourse, there are alot more things like shape, flow, returncone placement and so on :-)