My two cents.
Assumption 1: Not necessarily. Coaches miss on players all the time, and some players who were recruiting afterthoughts exceed expectations. College baseball teams only need around 17-18 very good players to do their jobs extremely well to carry a successful college team. My personal opinion is leadership and team chemistry is overlooked while skills & talent evaluation is overvalued.
Assumption 2: Not necessarily. Coaches make position decisions all the time weighing offensive and defensive skills. Typically position playing time is won in the Fall. Players have to keep their performance up or that is going to change. The quickest way to put doubt in the coaches head is to struggle with the bat, glove or miss signs. Different players have "varying amounts of rope" they are given. Then it becomes a matter of time before somebody else is put in the lineup. Also, coaches have a number of players that can play multiple positions, so there are always many lineup options for coaches.
Assumption 3: I can agree with that. Competition for playing time is incredible challenging in college at almost all levels.
Agree with CollegeBaseballRecruitiungGuide that coaches value their jobs above all else. If you are looking for what motivates a coach, I'd start there. The more competitive the conference the more motivation to find a recruiting edge.