So I guess your thesis is that by allowing LMI to maintain feature parity, that fragmented the market meaning neither company could survive? (We're ignoring the Xerox and Texas Instruments lisp machines obviously)
But this is ignoring the point that while this was happening the Mac and the PC were already in the market at a tenth of the price of any of the lisp machines and were selling by the bucket load. Essentially the PC revolution was already well underway before Stallman even started his hacking.
Lisp machines failed because they were selling high end limited use hardware running software that was good for a narrow range of highly specialised uses, but far too resource heavy to be economically viable for most users. The VAX for example was a far better machine for nearly every real world task except at running a single niche programming language.
If you really think single programmer stopped a $70,000 single user machine from derailing the PC revolution and kick-starting whole new world of computing heaven then you and I have a very different definition of "cheap" and without cheap computing we wouldn't be 50 years ahead, we'd be 40 years behind.