It's also very naive to think that these companies will continue to innovate. Once monopoly is achieved rent seeking becomes more profitable than innovating.
Where I live almost nobody uses LinkedIn. Many of our clients that do use it, have either been phasing it out or are simply not engaged with it in any way.
"Try getting a job without LinkedIn. Try buying a phone that doesn't run android or iOS." Your argument here would apply to everything then, why restrict it to "techno"? Try driving a car without buying gas from a small number of oil companies. Try using electricity without going through utility monopolies. Try using a credit card without going through... yada yada.
Does that mean we currently live in oil-gas-electro-feudalism? If you really think that, then your fundamental argument is: 'the social order is the same as it's always been', which just seems unnecessarily reductionist.
The term techno-feudalism is clearly politically loaded rather than empirically descriptive, and I think your response makes that pretty clear.
The whole argument hinges on falsehoods. They argue that participation is optional in the current web ecosystem and that's just simply not true, not only for the web as a whole, but individual fiefdoms too.
Try getting a job without LinkedIn. Try buying a phone that doesn't run android or iOS. Try selling an app without sharecropping an app store. Try running a browser that's not based on chrome or Firefox.
And there's others with slightly more choice, but not a lot, email, social media, link aggregation, music platforms. All with just a small few main choices.
And the other argument is that feudalism stiffled innovation with its rigid hierarchies, that that's exactly what we have today with a few platforms having all the network effect, and killing off innovation. Small Web is dead. Small forums are mostly gone. Used market place is hidden behind a Facebook login wall.
Technofeudalism is here, you have no choice.