I have been a (graphic + communication) designer for almost four decades and even learned to hand code websites in the early nineties, when the WWW was in its infancy, because I needed arguments when the programmers en tech guys tried to no-no my design choices and ideas. I have tried my best to keep up to date with new tech and software until I quit working, so I think I have some insight and useful (?) comments…
Yes, the Festool sites needed major upgrades. They surely needed better cross platform compatibility. Hence the 'modern responsive' design, that is ubiquitous (alas), with its modularity, low information density, simple design and coarse typography. But for a mainstream business conformity is an easier choice than a more innovative approach. Let's just say that the design is not bad.
Yes, rolling out a new site is a risk. But it has to happen eventually. Removing a bandaid comes to mind. Just do it quickly, the pain will fade sooner.
What has made this roll over painful is that apparently the back end appears to have been underestimated, eg the way the data have been organised and can be accessed. In the course of years and years of adding data mistakes are made. Databases differ in the way data are 'boxed' and described. When one tries to have data from all kinds of sources to fit into one model there will be glitches. And I think in this case the number of glitches was far greater than everyone expected & far more manpower had to be allocated to fix things.
If Festool had acknowledged that, the furore would have been far less than what has happened.
And then there is the design and usability aspect of the new sites. Responsive design is a fairly new branch of web design. It still needs to find its way. It needs to develop, like all other forms of communication design have. I am not a big fan, because as a designer I dislike the limitations it has. But just remember that it took over 200 years for newspapers to 'discover' the concept of the headline. Or the way the first websites looked, compared to nowadays. Thankfully things move really fast in the 21-st century.
It may take a while for us to get used to the new, but we surely will.