That only ever applied to broadcast media (and maybe only to prime-time TV). Publishers of the written word have never been required by the US government to grant equal time.
>For most of the history of the United States free speech has been more limited than it is today
I don't know what you could mean by that unless you are referring to the fact that before the internet became mainstream, you had to own a printing press or something like that to reach a mass audience.
https://en.wikipedia.org/wiki/Comstock_laws
Just a decade ago free speech rights were expanded to include corporations:
https://en.wikipedia.org/wiki/Citizens_United_v._Federal_Ele...
In case anyone tries to claim that the founders intended for the most expansive possible understanding of freedom of speech, the fact is that one of the earliest laws passed in the United States was a law that censored criticisms of the Federal government (in an attempt to crack down on foreign misinformation campaigns):
I'm not sure whether that proves your point. The wikipedia article says that it was controversial, caused the federalist party to lose the following election, and ultimately expired after 4 years.
You can also argue that it was defeated by the same men who ratified the constitution, and that the "free speech" side ultimately prevailed, therefore they really did mean free speech to be that expansive.