Yes the big tech companies have too much power over expression and "content."
When prominent people such as Donald Trump are banned from using the platforms, the important point is that they get away with so much more than "normal" people before they face any consequences. These platforms privilege the powerful, while normal people get suspended or banned for much less, constantly, and nobody thinks it's Very Important.
Of course they have to have some sort of moderation rules/guidelines, as every internet forum owner realizes eventually. There's no way to enforce those guidelines in a perfectly consistent manner, but powerful people get more leeway, so, again, their "censorship" is not the moment to get upset about this stuff. They get to break the rules many more times.
All this was solved in The Great Usenet Flamewar of 1994.