Disagree, because street space is limited, whereas there are a multiplicity of websites you can go to. It isn’t just a matter of personal websites. There’s a Twitter-like, Gab, which can be used. The president and his multi-million dollar campaign apparatus could easily strike a deal with Gab to host some more Gab servers and get their message out via Gab to anyone of their twitter followers who wants to sign up.
Never mind that Trump is not actually being censored on twitter in any way - his message still went out to all his followers, simply with an appended notice that Twitter itself considers the message to be factually wrong.
EDIT: this is like saying that the President has the right to publish whatever content he wants in a specific newspaper. Back in the day, a city might have a dozen newspapers - they could each print what they liked and if they decided not to print a person’s letter to the editor, that was no violation of free speech. Or if they print the letter to the editor with a note explaining they disagree with it, that certainly doesn’t violate free speech either.