I think the poster is saying it's not really a single point if no return and therefore isn't a great analogy. Crossing the Rubicon was about a single act that so broke the status quo it was impossible to undo that. This is more about the accumulation of a bunch of small steps making minor adjustments to the status quo instead of a singular act.
That's why I would favour "milestone". I understand what is meant by the "Rubicon" statement though (it's not about a river). Separate from if I agree with it or not.
Yes, milestone would be better because it is an arbitrary point that doesn't need to have some special significance other than the fact it is easy to detect when it has been reached.
"Today, the phrase crossing the Rubicon is a metaphor that means to pass a point of no return."
https://en.wikipedia.org/wiki/Crossing_the_Rubicon
Overhyped or not; that's a perfectly valid metaphor to use to phrase it.
I'd go with "milestone" which is less hype, but is also a metaphor, as no actual stone marking out a mile will be involved.