I posted a thread about this some time ago if I remember correctly. Back then, the same criteria as in the replies to this post were advanced, to qualify the "limits".
I suspect that the many (negative) opinions about "lightweight" are purely subjective and probably anecdotal.
I am a hillwalker, neither SUL, lightweight or anything else. I carry only what is needed for any specific trip. I do most of my hillwalking in winter and I carry more in my pack then, than I do in summer. With the benefits of modern materials and technology, these "minimum" requirements are getting lighter year by year. I am coming up for my 45th year of winter hillwalking in Scotland and my pack is much lighter than 10, 20, 30 or 40 years ago. The equipment is not only better, it is also lighter ( except my crampons, which are more or less the same).
The premise that lightweight gear isn't up to the rigours of Scottish Winters is absurd and doesn't merit debate.
Yours aye