The calculus also doesn't seem all that clear to me. A alternative calculus: Build something new on top of someone else's idea (stand on the shoulders of giants) or spend all your time and money reinventing a perfectly good wheel so that you can do it in a slightly different manner purely for legal reasons.
If we assume free licensing then you might as well cut out the middle man and abolish patents.
A case in point is China. It used to just produce low-value-added manufactured products, and it had little IP protection to speak of. But as China has moved up the value chain, it has passed IP laws and built out a court system to enforce them. It has rapidly become one of the most active venues for IP litigation in the world. But if there were no Chinese R&D to protect, there would be little reason for China to build out this system.