Even if everything about search was open source, how would an upstart competitor possibly compete on the hardware front? A single Google-style data center would imo be an insurmountable capital cost.
if there were an anti-trust court case, maybe a court would decide that Google is required to allow, say, a restaurant review site, to use Google Cloud on an equal footing with Google's own restaurant review service.
it reminds me of the decision where ATT was ultimately required to allow user-owned telephones to connect to its wired network. (in earlier times, ATT only let phones leased from and owned by ATT to connect to its network)
You could say the same about shipping companies, airlines or car companies. Yet, competition is everywhere despite high capital costs. Even space exploration has competition. High capital costs aren’t anti-competitive.