I think the reasons provided are valid (namely, faster blocking with less data flowing through extensions), whether or not you think they are good enough to outweigh their disadvantages.
"Their study --which analyzed the network performance of ad blockers such as uBlock Origin, Adblock Plus, Brave, DuckDuckGo and Cliqz'z Ghostery-- found sub-millisecond median decision times per request, showing quite the opposite of what the Chrome team claimed."
What are they really optimizing for ? The sub-millisecond times per request is barely noticeable, and on any given day its much preferable to ads tracking you everywhere on the internet!
The only evidence you offer is anecdotal. I'm having a hard time imagining perceptible differences in sub-millisecond response times so either you or the study are in error.
And just to reiterate other comments: yes, Safari is probably able to block ads just fine now, because they modeled the engine according to capabilities needed right now. However, it comes at a huge cost to innovation and creates yet another barrier of entry guarded by a large corporation.
Taking all of that in account, it seems unnecessary. The looming threat of ulterior motives from Google remains ever-present.
Looking at the WebKit implementation, the authors are shipping their own regex engine for whatever reason. I doubt that it beats the battle-tested re2 engine by large margins, if at all.
The reason for not allowing intercept the connection was security: the current API allow the extension do many kinds of mitm
Very true! Especially if the network impact is of the order of sub-milliseconds.