The legacy technology is also privacy-protecting in the sense that normal ad-blocking on iOS doesn’t use any third party JS filtering or reading of data on the page.

It breaks down because there are a ton of workarounds sites and ad-networks implement so it’s not super effective compared to MV2 ublock-origin

The privacy aspect is big. Even if content blocker extensions technically aren’t as capable, they were nice because they could be installed with impunity regardless of the party responsible for developing them. It’s a tradeoff.

In practice I’ve found them to be largely effective except for the most awful sites that I should probably be finding alernatives to instead of using (vote with your eyeballs), which is something I do even where “real” uBlock Origin is an option.

Only in theory, not in practice. Every Safari adblocker I've seen also uses scripts and requests permission to "modify data on all websites", because you can't effectively block ads without that (especially pre-18.6). I assume most users grant it.

So actually, you had closed-source extensions with full access to every webpage. Literally zero privacy benefit compared to the status quo ante. I doubt Apple thought it through.

Yeah but we are comparing that against MV3 uBlock Origin Lite which is the subject of this article. They are the same in terms of privacy protection.