Leaving out those things wasn't an accident or ignorance as Alan Kay claims. There were a lot of very conscious design decisions involved in the web -- again see "Weaving the Web".

He may regret that the web has evolved into walled gardens, but what could he have possibly have done about it? There's to prevent that decades in advance, at least not without strangling it from birth.

But, your argument is perilously close to begging the question that the success of web is a good thing. Now, I happen to think that the web is a net good (no pun intended), because (among other things) it helped break Microsoft’s hegemony and continues to force OS vendors to provide and support a standard universal computing platform (albeit a crippled one). But, it’s also arguable that the success of the web may have set personal computing back by a few decades, while also exacerbating a bunch of other problems like wealth inequality and reduced privacy/sovereignty, because it turned the Internet into a big modem.

I’ll take a look at Weaving the Web; thank you for the recommendation. To you, I commend Jaron Lanier’s Who Owns the Future.

he rails against the walled gardens while at the same time putting things into the standard, like EME, they powers them.

The W3C has to negotiate with industry. But, unfortunately for us that care about the open web, its position is weak.