“Working is only shayach for people who can work every minute of all working hours that they are supposed to (any minute during working hours not working is geneivah.)”
That is true… a person is not allowed to work in a place where it is inevitable he will violate geneivah. However, there is much more flexibility when it comes to careers. Some have longer hours, some have shorter hours. Some don’t have hours requirements but you have to make a certain amount sales or money, or have to produce a certain amount of goods. Sometimes a person is self employed, or the management monitors how he uses his time and any time he wastes is his lost money and is not geneivah. I’m sure there are many other situations as well. A person must choose a job or career in which it’s realistic that he will not violate geneivah.
Kollel is usually a lot more straightforward. It’s 2 or 3 sedarim of a few hours each, and a person must learn that entire time… no breaks, that’s what bein hasedarim is for (obviously once in a while for something extraordinary is not (in my opinion) geneivah, though it should be discussed with the people giving him the paycheck). Additionally, sechar is based on effort so no matter how much or how little one learns, if one is being supported, he must learn the entire time on a regular basis. If a person cannot do that, just like any other job, if one cannot fulfill his duties, should not choose that profession.