This is indeed true, and a problem, and if you have ideas for how it can be improved, I'd be all ears.
But, I've not found any country/region/system that doesn't have some level of this problem. The US's system, of required public formalities for certain charges to proceed, & certain guarantees of time limits, & avenues for release/acquittal, is pretty strong compared to anywhere else. (In the Netherlands, a software developer has been in custody for a couple months now without any specific charges/case being revealed to him or the public.)
And, it's kind of inherent to any system for there to be some margins-of-abusive-discretion that are hard to eliminate, and time-limited steps-in-a-judicial-process where unavoidable "punishment" comes even from a process that hasn't decided yet. So mentioning the mere existence of such unevenness doesn't really say anything, either way, about the relative value the US culture, or legal system, puts on free speech.
What does shed light on the value the US puts on free speech is whether such irreducible annoyances are larger or smaller, with respect to speech, than other countries and other eras. And at every step of US history, even dark days like say Wilson's persecution of WW1 draft-resisters, or Hoover's mid-20thC persecution of civil rights movements, the US had more space for speech, more defenses for those accused of speech-related offenses, and larger cultural/social support (in both legal/political action and the commercial 'blocking-and-tackling' of actually publishing & disseminating speech without outsider veto) than almost anywhere else.
That's where people should be able to see the real, high, & enduring value the US has always put on free speech, if not neurotically obsessed on only negative examples, & scattered hypocrisies, blinding them to relative-magnitudes.
If Americans have not consistently enjoyed equal free speech – but even in such inequality, almost all Americans had far more free speech than they'd have had anywhere else – then that's more a knock on the US' value of equality, while confirming its leading value of free speech.
The last 2, gets a bit self-congratulatory. Jim crow laws (until 1965). Emmet Till didn't get much rights to free wolf-whistling https://en.wikipedia.org/wiki/Emmett_Till And plenty more.
"If Americans have not consistently enjoyed equal free speech [...] then that's more a knock on the US' value of equality"
If you don't have 'equal free speech' then you don't have 'free speech', full stop.
Not at all. Free speech is not binary.
More is better, & the cultures that have consistently had more speech tolerance than elsewhere - like the US, in its formal documents & actual practices – are showing that free speech is a more central value to them.
If you had a country where 95% of individuals had absolute freedom of speech but 5% did not, is that more or less free than a country where 100% of people had near-absolute freedom of speech?
What about when those percentages collide? When the free speech of the haves results in the suppression of the have nots? And historically the freedom in US has been in theory and not in practice what with how it's been used to hunt down perceived communists, minorities and dissidents.
The best possible evidence against the idea that more == better is played out in the various sites that try to have absolute freedom of speech. The end result is that you get a large amount of people that others either do not want to associate with or get chased out by the rabid angry mass. Websites and forums form a sort of microculture that prove you need some guardrails to prevent the bus from going off the edge.
But yes, more free speech – in terms of being able to honestly express your opinions, without the threat of punishment by the state – is better. From any particular state of "absolute" or "near-absolute" free speech, giving some people extra freedom to speak without state punishment is an improvement.
We were talking about the US, as a polity/legal-system. Private forums can and will set their own standards. But the US public-sphere, and what the government can get away with punishing, has for centuries had world-leading free-speech guarantees.
Race is a far less salient variable affecting speech, in the US, than income or education.
Many of the US's most fearless speakers, often relying on our legal protections or cultural appreciation, especially with respect to criticizing the powerful, have been from categories of people that are otherwise economically disadvantaged.
And, their practice of free speech, aided by the underlying high value from the culture & legal system, has helped to correct those other inequities.
Which again, you ignore that we had (and in many places still have) an amount of people which simply did not have the same free speech rights that you say America was founded upon.