I'd like to give my thoughts on this matter.
Joint strenght/speed/weight on the default tori is the most important thing in the whole game.
The default tori will be the foundation of 90% of the mods and will be the standard.
As it is the standard for gameplay it's not something to look over just quickly and "let people decide the joint strengths".
There is a reason body mods never took off, not because they weren't good enough, but because even the slightest adjustments to joint power drastically changes movement.
Re-learning the tori's movement for every individual mod isn't something people are really willing to do.

The speed also has massive impact on the actual direction of the gameplay.
Faster/more powerful overall Tori's will make the gameplay less realistic and controlled as you are able to launch with single joints easier, while slower Tori will make the gameplay more "realistic" and things like blocking and body control become more important.