Sure and as an op-ed, the journal itself makes a decision whether it wants to front that opinion. The journal has stopped being close to Mr. Greenwald's perspective. Sure, maybe they changed the rules on him since it had become their publication. But that's a King Lear story, not a journalism story.
"You broke your promise that I'd have unlimited publication rights" is a sad story of broken promises but it's not a story of journalistic decline.
The point of op-ed's is that they differ from the publication's opinion. That's why they're opposite the editorial page, to provide a contrasting viewpoint. They've got their own columnists and the board for that.
The point of op-eds is they reflect a range of views the editors think is interesting, varied or whatever. Op-eds are still a matter of editorial decisions - obviously, papers don't just publish anything by anyone.
Maybe this is breaching the agree Greenwald had with the editor(s). But independent op-eds able to say whatever they want isn't a principle of journalistic integrity. Questions of that sort revolve around whether you lie or misdirect or run paid articles and so-forth. That you refuse to run an op-ed right when your writer really want it published is a wholly different question, one clearly about the paper having indeed evolved to a left-liberal position while Greenwald maintains his conservative/Libertarian principles - ie, the argument is political.
Glenn said he also tried to publish it somewhere else and they forbid him from doing so, even though his contract says he has the right to publish stuff elsewhere if The Intercept doesn't want it.
They said "Our intention in sending the memo was for you to revise the story for publication. [...]
It would be unfortunate and detrimental to The Intercept for this story to be published elsewhere."
That's not forbidding him from publishing it, it's expressing regret that he appears to be unwilling to address the editor's comments on his draft.
Interesting, I didn't know that. But "detrimental to The Intercept" seems a little foreboding. It could be interpreted as them saying he's doing his job wrong if it's published elsewhere, and if he does his job wrong, he might assume there would be consequences.
"You broke your promise that I'd have unlimited publication rights" is a sad story of broken promises but it's not a story of journalistic decline.