I think your analysis of the shifting technology landscape is largely on target. However, I'm not convinced that the true root of SGI's failure was the technology. Clearly their tech did need to evolve significantly for them to remain competitive but that's a transition which many companies successfully make. Even though SGI chose not to evolve the tech soon enough, fast enough nor far enough, I suspect they still would have failed to survive that time period due to an even more fundamental root cause: their entire corporate structure wasn't suited to the new competitive environment. While the "desktop transition" was most obviously apparent in the technology, I think the worst part for SGI was that the desktop shift changed the fundamental economics to higher volumes at lower costs.

SGI had invested in building significant strengths and competency in its sales and distribution structure. This was one of their key competitive moats. Unfortunately, not only did the shift in economics make this strength irrelevant, it turned it into a fundamental weakness. All that workstation-centric sales, distribution, service and support infrastructure dramatically weighed down their payroll and opex. This was fine as long as they could count on the higher margins of their existing business. While it's easy to say they should "just layoff all those people and relaunch as a desktop company" that can't be done in one quarter or even one year. It requires fundamentally different structures, processes, systems and skill sets. Hiring, training and integrating all that while paying for massive layoffs and shutting down offices, warehouses etc takes time and costs a lot of money.

Worse, once their existing workstation customers saw them shutting down the SGI the customers had bought workstations and service contracts from to become a different kind of company entirely, sales revenue would have taken an overnight nosedive. SGI's stock would also have tanked far more immediately than it did as the fickle stock market investors sold stock they'd bought because SGI offered a specific risk/return expectation which just became much more "risk" and much less "return" (at least in the near-term). In making such a dramatic move SGI would have effectively dumped much of their current quarterly revenue and the value of one of their core strengths - all at the same moment. Thus turning them into one of their emerging startup competitors with all of a startup's disadvantages (no big ongoing revenue streams, no big cash pile (or high stock valuation to leverage for cash)) yet none of a startup's strengths (nimble, lower-paid staff and more patient venture investors).

The point of my earlier post was mainly that a true disruptive market shift is nearly impossible for a large, established incumbent to successfully survive because they basically have to rapidly turn into someone else almost overnight. How can a champion sumo wrestler survive a shift so dramatic that their sport quickly turns into a track meet? Even seeing it coming doesn't help. How does one even prepare for such a shift since losing mass turns you into a bad sumo wrestler long before you even start being a viable sprinter? As Christiansen observed, such disruptions are often enabled by technology but the actual cause of incumbent death is often due to the shift turning an incumbent's own strengths into weaknesses almost overnight.