During a proper development beta phase (as opposed to it being a glorified pre-release demo) where things were actually beta tested, added, and iterated upon on a weekly basis at longest, plenty of things were tried. A great many things changed with alarming frequency all the way through the premium beta (and even more frequently before that, from what I was told). For several months, practically every day when Monk and I wanted to play, we had to wait for updated builds to download and find ourselves navigating new features. When things were found to be ideal, of course, they were left along. Why would there need to be sweeping changes to things that - by and large - didn't require changing by that point? Remember, when you got the game it was (by the standard of the development) on the cusp of launch, and by that point many of the features were already solidified. Much of the standard beta and gamma were intended to be - and in point of fact were - working on scaling and backend aspects of the game that could only be tested for capability in a truly live environment.
The release cadence and state is exactly what was set forth in (and even before) the Kickstarter campaign, where there would be 'several content patches' for the core game and expansions. Look over the last year and it's plain to see that with things they've added both with and in between point releases, they very much have stuck to this, delivering in a reasonable and iterated timescale precisely what they said they would.
Just because there aren't still massive things added every week, it's not 'slow'. It's a deliberate, thought out and methodical release process with a careful consideration to not push things before they're ready with astounding transparency into the development and iteration process when they *are* being developed. Following entirely from what Braben and the Frontier staff have always said, that they'll be taking a 'when it's done' approach, with each year intended to be building upon the last.
Furthermore, many features that are complete and ready to go aren't immediately pushed, instead allowing multiple complementing features to be released simultaneously, in the process avoiding what I have termed the CCP Effect.
Of course, because I have no grip on reality I may have hallucinated the entire premium beta phase and the year and a half or so before that when I was following the development, something which I may still mistakenly believe I do when I'm in point of fact reading a blank page or something. We will never know.
"The best laid plans of mice and men often break down to inherent cross-species communication barriers"