How to reduce spacing between icons on quick access toolbar?

Understood that it takes guts and efforts to push changes through  and there will ever be some resistance to any change.  But it is conceptually wrong to push changes that makes people less productive. Not all of them will be less productive with new spacing, as not all of them using Quick Access Toolbar. And not all of those who use it, usually load it to the extent, at which new spacing becomes an issue. But most advanced and most effective users are affected.

The fact that Microsoft intentionally blocked that feature in the software, where it was fully implemented, tells us that they don't care about productivity maxed out by their most loyal and most advanced users. The don't care about productivity at all. But they dream about market penetration and reach, trying to cover most of those who barely need the office at the price of betraying they most loyal core customer group.

This is the same type of move they did when they first introduced ribbon and dropped some previous menu organization features.

Seriously, why on Earth Microsoft's investors would care about  how productive John's work is when intensively using Microsoft Office 2016, while it is possible to attract 5 more new light users by showing new Chip and Dale animation theme in the space previously utilized by geeky buttons and switches?

John's productivity doesn't improve company's capitalization, but 5 new users do.

Once we understand that Microsoft is here not to serve us, who need the software, but is here to serve their investors, we would stop complaining about being betrayed

Touch is more convenient for many tasks, and it's here to stay.  So long as everybody gets to make constructive criticisms, there is no point in complaining about it.  

Touch is only more convenient if you have a touch enabled device.  I, and many other, maybe even it is still MOST, Office users still do NOT have touch devices! (Yes, that will change some time in the (near?) future.)  Unilaterally forcing a design change that does not help us is the opposite of convenient because it removes buttons from M Y QAT!

Whether you call it "constructive criticism" or "complaint" we users have to provide feedback because that is the only way we can try to get changes.  In this case all of the feedback actually got us some change, some improvement.  A return to 2013 spacing, even though most who asked wanted to go back to 2010 spacing.

I agree, it seems absurd that desktop applications have a touch-screen interface forced on them. This is dopey.

That's not the problem here:  there *is* a difference in the spacing between the touch and non-touch settings.  It just so happens that they made the separation between icons too wide on both settings.

The mouse was invented in 1941 and patented in 1947.   Touch is more convenient for many tasks, and it's here to stay.  So long as everybody gets to make constructive criticisms, there is no point in complaining about it.

That's what I said in the edited update of the post you quoted. In Mouse Mode the spacing of buttons on the ribbon is smaller than in Touch Mode, but the spacing on the Quick Access Toolbar does not change. The original post describes how Mouse Mode worked in an early technical preview, but Microsoft later removed the behavior.