what you are describing here is not a system, it is a random, chaotic mess.
distributions are made by "big picture" systems people. they want the ENTIRE system to work smoothly as an integrated whole. i.e. they're mostly systems administrators rather than programmers (although there's a lot of crossover there's also a very obvious distinction between the two).
applications like firefox, chrome, etc are made by programmers. their focus is far narrower, all they really care about is their application - even at the expense of the larger system that it will be installed on.
this is not to say one kind of developer or the other is "better" - they're not, and BOTH are absolutely essential. but software works best when programmers and sysadmins work together, rather than try to work around each other.