Microsoft only has itself to blame for all the backlash and negativity regarding legacy Start button functionality.
The reason being that prior to the Modern UI, Windows has a very long history of organizing apps and document links via a nest of standard and user-definable of folder structures. When a typical legacy app is installed, it creates its own Start menu group (folder) into which it places its icons. Enterprise-type apps were the "worst" in that they were usually so "complex/functionality-rich" that they usually had a multitude of icons.
So now Microsoft brings us the MUI. Personally, it's definitely my preference and every chance I get, I retire a legacy app for its MUI version or a MUI app that provides the same functionality. However, with Legacy Windows' long history, obviously the vast majority of Windows apps are still legacy apps that have been built around the Desktop. Thus, most Windows apps and their document links are still organized using that legacy Desktop folder structure motif.
And how does Microsoft address this in the MUI Start Screen? By implementing a horizontally-scrollable list of Live Tiles ("icons"), organized only by a user-defined Group header name. Although that works, it by no means provides that Start menu folder structure nest of apps/document links organization.
Although one can always re-create that nest of Start menu folder structures on the Start menu using various Groups, the problem is that the MUI Start Screen is flat--scrollable only horizontally; i.e., no nesting/drill-down capability. As a result, re-creating some people's entire Start menu structure would result in an extremely wide/long Start Menu screen. Uggh!
That's definitely what it would be in my case! As I stated, I'm sold on MUI and initially I tried to re-create my Start menu structure on the Start Screen. Forget it!
It was just ugly and not very functional/user-friendly. The bottom line is that Microsoft should have implemented (and still needs to do so!) a Group ("folder") structure nesting capability in the Start Screen. Not everyone wants to forever scroll horizontally just to find an app!
In the end, what I settled for was having 99.999% of my Start Screen with MUI apps. When I need to use Desktop apps, I switch to the Desktop and use the Start toolbar. I am equally not a fan of cluttering my Start toolbar with a bazillion of all possible apps/document links that I use; it only contains the frequently-used ones. So when I need those infrequent ones, I use the great Search feature of the MUI Start Screen.
For me, that's an acceptable workaround to organizing and accessing all my Desktop apps/document links, but I know for sure that will not suit everyone.
Had Microsoft provided that legacy Start menu nesting folder structure functionality into the MUI Start Screen, then they would have been able to refer the critics to a practically seamless workaround/equivalent using the MUI Start Screen.
But, sadly, they chose not to and this is why we are where we are today on the issue. They only have themselves to blame.