Yeah I reworded it - I meant Blink. And no, I'd argue that just because it's open source doesn't change that it's an antitrust-worthy browser. The obvious problem being the conflict of interest in developing a browser (which is meant to serve users) and an advertising platform (which is meant to serve business customers). That alone should have prevented Google from entering that field, but here we are.
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In a technical sense, Chrome is a monopoly though. The development of Chrome moves at such a rapid pace that only Firefox can keep up (kind of, Firefox had to give up on anything involving PWAs to do it and they take a large sum of money from the big G for putting their search engine as the default).
Similarly, just look at how many web RFCs amount to "this was implemented by Chrome and technically a Chrome fork is a second implementation, so it can be OK stamped", which has squeezed the market for third parties to be able to develop their own browser just by making the amount of "required" features so large nobody could meaningfully implement them.[0]
And then there's the utterly dismal state of the Android platform, where Google just uses their control over OEMs and the ROM to outright prevent anyone from easily replacing the System WebView (the browser Android uses to render stuff "in-apps", basically if you've ever used an app that seemingly opens external links without launching chrome, that's the System WebView) with a non-chrome engine (basically, Google lets OEMs specify a hash on what the System WebView should be - almost all mainstream OEMs lock it to the Google implementation -or Chrome Canary which is just the same fucking browser-, leaving the only option to circumvent it to be rooting, which has its own issues and limitations).
There's no meaningful maintained alternatives to it either (Mozilla's work on GeckoView only targets individual apps, not the system version; Vanadium and Mulch are both just Chrome forks that implement it as part of a larger custom ROM but in the end are only competition in the same way GNU IceCat is technically a competing browser - they're openly tied to the Chromium upstream because they lack the manpower to do it on their own. The Vanadium dev also stopped anyone from using his work in the future by setting his System WebView implementation to GPLv2-only to prevent folks from forking it), since nobody wants to bother.
Just being open source doesn't prevent a company from using their leading position and size to muscle away all the competition.
[0]: https://drewdevault.com/2020/03/18/Reckless-limitless-scope....