I wasn't a fan of NaCl, and WebAssembly (for example) is a much better fit for an open web, but it was at least platform agnostic (if support was provided by the vendor) and ran in a reasonably strict sandbox. ActiveX was neither of these things.
All that said, having any one browser be the standard is as terrible for the open web now as it was in IE's heyday. Just because Chrome is less awful doesn't solve the single-vendor problem.
"If support was provided by the vendor" is a big if...
Google was well aware of this inherent flaw but pushed NaCl regardless while at the same time promising for years that PNaCl would eventually solve all problems. PNaCl never really materialized, I think, and it feels like Google was throwing a smokescreen there to boost support and mindshare for NaCl.
I wasn't a fan of NaCl, and WebAssembly (for example) is a much better fit for an open web, but it was at least platform agnostic (if support was provided by the vendor) and ran in a reasonably strict sandbox. ActiveX was neither of these things.
All that said, having any one browser be the standard is as terrible for the open web now as it was in IE's heyday. Just because Chrome is less awful doesn't solve the single-vendor problem.