The other Huge issue is that, while the combination of a skid steer and mini-ex would be the ideal solution the skid steer alone is more than three times the cost of a fully loaded RK37. (A Deere 333G is just over $100,000 plus attachments while a full tilt RK37 with attachments is $33,000 or about $650/month with insurance) Even buying used it would be out of the realm of possibility. He has no desire to take on a full time excavation business, which is what would be required to pay for that type of equipment.
Equipment acquisition cost is relatively low relative to repair and employee injury cost over time.
The point is that there a number of tasks around the jobsite that a compact TLB could do. Larger jobs would still be done by sub-contractors, but there are more than enough small jobs that the RK37 can do that it would easily pay for itself and then some, not to mention not having to wait f or a sub to show up to do a 30 minute job. He does a lot of remodeling work so there are many times he is calling in a sub to do less than two hours work and with the economy improving it is becoming harder and harder to get them to show up for anything much less a small job. That significantly impacts his ability to service his customers. As mentioned before, it is $250 minimum just to get equipment on site, before they do anything. With multiple jobsites going at once those fees add up. If only 3 of them per month are eliminated that more than pays for the tractor.
My tractor is 3,700 pounds bare tractor weight. In my opinion a 3,100 pound tractor, nor a 3,700 pound bare tractor is stable enough on a construction site. Backhoe is excellent rear ballast.
I have worked construction as a plumber. Machinery is always overworked in practice.