Causality is inverted. The harm was done in electing to use non-free, proprietary, single-player data formats. I've been watching that error be made for 30+ years now.
Don't lock yourself in to that crap in the first place.
On the contrary, I wrote in my post that there was no free, open choice at that time.
In fact, XMLHttpRequest didn't become a W3C Working Draft until 2006 [1], before then it was a proprietary Microsoft extension. Canvas didn't become a standard until 2007 [2], until then it was Apple's proprietary trick. The DOM was the only API of what we now call the 'web platform' for many, many years.
Between 2000-2006, Flash, Shockwave, and Java Applets were delivering rich interactivity while the open standards were nowhere to be found. While we can and should celebrate that the 'web platform' is finally good enough to replace proprietary applets, the schadenfreude is unnecessary.
I didn't say the harm was in choosing a proprietary standard over an open one. I said it was in choosing a proprietary standard.
I'll allow there were few alternatives at the time, for in-browser, run-many-places interactive content. You could have ginned something up in JS, Java, or distributed binaries for your target platforms.
But if you find yourself gazing into the abyss of "well, I've got to use a proprietary standard to do that", you can be virtually certain of the consequence you've noted here.
(Not that open standards last forever either, but the track record is vastly superior.)
Don't lock yourself in to that crap in the first place.
Consider the pain an educational expense.