Thanks for the feedback.
I've continued thinking about it, and think I start to understand how a variation on the current system - option (1) above - might work.
This in conjunction with another post I've made today on a bug report that is not really a bug.
https://www.lfs.net/forum/post/2085863#post2085863
The point in the other thread is that the axes other than steering already operate over a limited amount of the controller axis output, in a way that cannot be controlled by the user.
Brake, throttle, handbrake : 0 to 1 over 5% to 95% of controller value.
Clutch: 0 to 1 over 5% to 65% of controller value.
So what I'm thinking now is that the confusing "-1000 to +1000" range might be converted to a simple percentage, and the default values could cover the other non-adjustable values described in the other thread (that would be removed).
So instead of -1000 to 1000 in the range section, the defaults would be:
Brake / throttle / handbrake : default min 5% / max 95%
Clutch : default min 5% / max 65%
Steering : default min -100% / max 100%
These defaults would replicate how LFS already works. As far as I can understand, these min and max values do not need to go outside 0% and 100% except for the steering which should be allowed outside this range (allowed range -200% to 200%).
I think this is quite obscure and my explanation might be insufficient and confusing. But anyway that's where I am so far. When looking in the code there could be further complications that make me backtrack and change my mind, but that is the nature of game development.