My point is the upselling abuse has been supported by many forumers
no, don't agree. I don't remember any post supporting that (at least from a regular forum member).
You can search yourself.

limit negotiation of a player to 1 move a season to reduce how far they can move up the tree.
yes, this is simple and logic (but don't know if the devs can work with that)

3. By itself, the division into "dark" and "light" skills leads to the fact that this can be manipulated.
definitely the devs should work this thing with skills/drills and training or else this would be just a Police and Thieves game.