User testing would have taken ONE DAY...Don't get me wrong, I agree with you completely about testing and there should be far more of it. It just isn't the world we live in. It isn't reality.
User testing might have taken only one day in your example, but reworking the software to accommodate the changes would likely have taken months. Then you have to test again and make even more changes.
All that takes substantial time and large cash outlays to pay for it.
These days, even Apple releases stuff first, then figures out what they need to change based on user feedback –– if they change anything at all.
They finally got the Apple TV remote mostly right after four attempts. Only the most recent one has a mute button on it.
Apparently Apple did solicit feedback from professionals for the current Mac Pro, and look how long that took to come to market. Years. Apple didn't care because the Pro market is a very niche and those users aren't as price conscious. Apple has plenty of R&D money to throw at the problem. I think it has mostly been a successful product, regardless of what the press might have you believe.
if you get too used to a lot of 3rd party customization you lose the skills to operate the same OS on a different computer.I don't, but I guess I could see how that might be a problem for some. Thing is, people who do a lot of customization wtih 3rd party tools are already adept at using their computers.
Also, how often are people switching the computers they use? Even as a computer consultant, when I have to work on someone else's computer that doesn't have the customizations I've made to my own, I only find it mildly frustrating. It's still my choice.
Most people use their computers alone, they aren't hopping around using those of others.
Lastly, "gunking up the OS" is my choice. I know what I'm doing enough to deal with the consequences. You like to run a spartan system with only a few 3rd party options, that is your choice. Don't take away mine.