Correct. They failed at monetization without pissing off their users. Partly because they did it earlier. Youtube was ubiquitous by the time they started pushing intrusive ads, so people either dealt with it, paid, or used an adblocker instead of just leaving.
That doesn't change that the "idea" behind Medium is good and that there's a market for a blogging platform that gives authors easy access to a large audience.
Good ideas aren't worth much if the business model doesn't work. They've raised over $100M and have pivoted multiple times. At some point you have to ask whether the idea is not a feasible one.
Alternate possibility: the core idea is a good one, but they raised too much money. Now they have to live up to an impossibly-high valuation and can't just be a blogging platform.
That doesn't change that the "idea" behind Medium is good and that there's a market for a blogging platform that gives authors easy access to a large audience.