Google's Widevine (streaming media DRM) is a great correlate to this. If you wanted to try and create a great, novel 4th web engine/browser; good luck. Many of the major streaming sites use Widevine. You can't build a browser to stream that content without asking for access to Widevine encryption. Google will not give it to you; they may, eventually, if you build up enough of a userbase, but what browser would be able to build up that userbase without access to streaming media?

Its less about building a bulwark around Google's technology, a clear monopoly, and moreso a bulwark around the Boys Club of Established Big Tech. Then Google can go to Congress and say "we have competition, look, Facebook serves ads".