It's just slow.
Consider this. If there was an operating system which could launch a program like firefox in less than a second while running a full blown desktop with 3D enabled on a 1GB memory, Core 2 Duo system wouldn't we call GNU/Linux as comparatively slow operating system?
Just because it happens that a common GNU/Linux installation is sometimes faster than all other operating systems, or at least equal to them doesn't mean that GNU/Linux reaches or even comes close to what can objectively be accomplished with the 21st century knowledge and 21st century hardware.
Sorry but it can do better.
So what am I going to do about it? Well pity, I after all didn't choose a path of software development, but rather of web publishing, so I guess what I *can* do is what I always do - talk about it, provide my own evidence and arguments and discuss it. And if there is a project which attempts to change things to the better, significantly better, without sacrificing any functionality (like most "lightweight" programs do) help with reports and testing.
The thing is most of the "lightweight" software we have is light only because it is stripped down of functionality under the justification that it isn't needed anyway, that it is bloat - that of course isn't always true and that of course is more like cheating than really improving performance of software.
But.. at the end of the day, I'm not an expert, but perhaps just a whining user (sometimes) so if the reality is much more entrenched than I think, if there is really no better way.. I guess I'll shut up.