Why do you say "steamroll"? They came in because they were allowed in. Are you now making the case that protectionism is good and EU/UK should prefer their own while blocking foreign companies? If it was that easy then why wouldn't they just do it to encourage domestic activity?
The rest of the world is not going to change just because we start to treat China the same way they treat everyone else. Perhaps you should read up on how India and other countries are also defending against China.
How do you think US corporations were able to grow to global scale without registering legal entities in the %95 of the world? Because due to the US pressure and advocacy for free speech not letting Facebook, Twitter, Instagram and others to operate was considered a matter of free speech in the pro western world. Russia and China did not played that game and had homegrown versions.
US is not going to win China and is about to lose the non-US wester countrieds by blocking TikTok. After the TikTok case no political activist will have credibility when the next dictator or would be dictator blocks Twitter. In places like UK/EU where local companies aspire to compete with the US ones you can expect much more hostile environment for the next US startup because no longer the issue would be a matter of freedom but national security.
US companies are welcomed because they provide investment, jobs, resources and opportunities that weren't otherwise available or developed domestically. This has absolutely nothing to do with free speech (which again isn't a law and isn't even the same in other countries).
China specifically acts against free trade and is now being treated the same way (after decades of being unfairly tolerant to them). This is no different than tariffs and sanctions against other troublesome nations. Nobody is going to start blocking US companies because of this.
It doesn't take huge technical skills that exist only in SV to build alternatives to US internet companies. The reason why China and Russia have their own alternatives but the EU and UK don't is because they let US steamroll into their markets. FB and other US companies were early or had better funding and got the lead, network effect kicked in and they dominated. When a country blocks you off, your funding and network effect is no more.
In other words, the moat of the US internet companies is not their tech but their network and that network can be made anaemic by countries who want to have their local alternatives, as seen with Russia and China.
Even in places where that tech expertise doesn't exists someone will build white label solutions and sell them.