I think 1 is too extreme of a change, though the spin time can probably be decreased by a smaller amount. I like the other changes mostly, though I've only tested them in Single Player (since that's what I mostly play). The 'running down slopes' change feels a bit weird and I'm not entirely sure I like it but in levels with big slopes that clearly were intended to be run down (looking at you, Easter) this does clearly improve things.

However, given the earlier response to a vaguely similar request I wonder whether these changes would not be better implemented as a mutator, assuming we can at some point load mutators in single player easily too? I think the position articulated in that thread ("JJ2+ will not itself rebalance character abilities") is a healthy one and some of the changes here do seem to go in another direction.

tl;dr
1 - Tone it down, then probably OK
2, 3 - OK
4 - Probably OK, though like minmay I have some lingering doubts
5, 6, 8, 9 - OK for the part of the game I play, but I think these may be too controversial to change across the board
7 - I don't 100% understand this one but it seems fine?