Yea, manual pumping is real weird right now.
When I set Vert Pump Assist to 100 and Semi Auto Pumping off and just roll back and forth in a half pipe with no other input, I see my character do the pumping motion/animation, and he goes higher and higher each time. With these settings, no matter if I press the triggers or right stick, it doesn't seem to make a difference, and the "pumping" trick never activates or vibrates my controller.
This makes sense to me. With Assist 100, your character is basically doing the work for you already, so there's no need to input.
With Vert Pump Assist 100 and Semi Auto Pumping On, I see the same behavior, except my character reaches speed faster. This makes sense to me too, since Semi Auto says "One pump grants full power".
Things get weird when you lower Vert Pump Assist.
With Vert Pump Assist to 0, and Semi Auto Pumping off, my character doesn't do any pumping at all unless I input, so if I just roll back and forth, I never gain speed, and just kinda stay at the same height. Currently I can't get right stick to do anything. It seems to make no difference to my speed if I squat with right stick. The triggers do however activate the pumping trick/vibration, and when this happens I gain speed. However, it seems like executing a full grab can actually hinder your flow and slow you down, especially on the way back down into the half pipe. I seem to get the best results when I only half press the triggers, so I never actually grab, but still squat. This is a really annoying way to play the game, but it does seem to get me actual speed.
With Vert Pump Assist 0 and Semi Auto Pumping on, things get even weirder. Sometimes when I pump I get a much larger speed boost, as expected, but other times I get basically no speed even though the trick/vibration activates. And some other times, the trick/vibration doesn't activate, but I get a huge boost of speed!?
So, what I'm seeing is that right stick to pump is just totally broken right now. And if you actually want to get big speed with the least effort, you should use Pump Assist 100, Semi Auto Pumping on.
If you want to manually pump, then you should use Pump Assist 0, Semi Auto Pumping off, and only hold the triggers part way when you pump.
Ideally you'd be able to pump with the right stick, so you don't have to half press the triggers, it would feel much more natural. And ideally manual pumping would consistently work with Semi Auto Pumping on. Those seem like the biggest issues right now.