Fitting things together is important, but it exists entirely for the purpose of creating things, which is ultimately in service of end users. Fitting things together is mostly an implementation detail.
Creating things is just fitting together new things. Rather then fitting together many new things that may overlap already existing things we should focus on fitting together an efficient unified system that use resource sharing to ensure a minimum of bloat.
In death of the desktop, interface expert Aza Raskin mentioned that his computer has seven copies of the spellcheck program with seven slightly different implementations of the English language. Building a user interface based upon command sharing rather then bloated applications will ultimately benefit end users.
Obviously better interop is a Good Thing, but we're talking about relative weights of good things. My point is that it's nonsensical to ascribe "fitting together" a higher weight than "creation", because "fitting together" is a subset of "creation".
Now as to the manner of creation: you're reacting against the "just hack it together" philosophy of ghc. But the alternative in ghc's mind, I think, was people not creating anything for fear of not getting it right, or not knowing that building something for themselves is even a possibility. Sub-optimal creation is usually better than nothing, especially when nobody else has to use it.
Fitting stuff together is hard, especially now when we don't have good protocols. While we're working on those, telling people who just need to get stuff done to "wait until we figure some stuff out" is not acceptable. Those people (who may not even be "Programmers") and their products will still benefit from "fitting things together" to some degree that depends on the application (OS or fart app?), but that needs to be balanced against the need to actually finish at some point, all of which is in the service of some non-software need. They just need to get it done with whatever works, whether it's Haskell, PHP, or a spreadsheet. That, I think, is the point ghc was getting at.
You got it backwards when you said "fitting together" is a subset of "creation." Creation is fitting existing unused materials together into a more usable form. I believe we should encourage people to fit together existing programs rather then encouraging people to build stuff "whatever the language, whatever the library, whatever the framework".
If everybody uses whatever framework without concern for compatibility it will inevitably lead to enormous bloat. I have no problem with getting things done quickly to fulfill non-software needs. However, when it comes to software one of our most important needs is to reduce bloat by encouraging sharing.