You're falling afoul of a common fallacy: that every rule needs to have every possible iteration of its boundaries spelled out. This is not the case.
To the contrary, it's counterproductive. The more subclauses added to a rule, the more there are to remember, and the more people think that because something isn't listed that it's okay.
But, here's the thing.
The only mod action taken was to remove the post and tell you that substack isn't a valid source for that C/.
That's exactly what a mod is supposed to do. You are still free to post on that community, with sources that are allowed. That's the exact opposite of power tripping, it's measured, responsible moderation.
You don't have to agree that substack is a substandard and questionable source for news. You can freely post things from there on any of multiple lemmy communities. That C/ is not a gatekeeper for news on lemmy at all. Things being barred from there do not prevent them from being seen. So you can't claim that it's power tripping my that metric either.
But, I'm going to repeat and rephrase the opening of this comment.
It doesn't matter how well written, how well spelled out the rules are, someone is always going to disagree with them, think they don't apply to them, or just try to play rules lawyer with them to get around them. Trying to continually chase new rules, and rules expansions is a sucker's game, it can never succeed.
That being said, if Jordanlund or any other mod of that Conley community, or any community, wants to try and streamline their rules, I'm always glad to try and help jigger the wording of things. And, that rule probably does need clearer language just to reduce future complaints. It is a bit vague considering that "news articles" is not defined, and the colloquial usage of the term differs from a more formal one.