Rewatching TNG and one line in Chain of Command made me laugh out loud.
During the negotiations with the Cardassians on the Enterprise Riker loudly exclaimes “the Federation will not start a war.” Oh please, the Federation have started almost every war we know they’ve had. Especially the Dominion War.
Burnham started the Klingon war and Starfleet started the Dominion war.
Focusing on the Doninion War, Starfleet discovers a stable wormhole to the Gamma Quadrant and starts exploring it. Fine, fair enough.
However in 2371 the Dominion warns Starfleet to stay on their side of the galaxy, stop planting colonies and stop violating Dominion territory. Again, fair enough.
After all would the Fedetation allow the Romulans to explore Federation space freely? Of course they wouldn’t. But the Federation expects to explore the territory of others freely because Starfleet believes they have a RIGHT to explore the galaxy and if that means crossing borders then so be it.
The Federation then gets all pissy when the Dominion sees them as such a threat they ally themselves with Cardassians to establish a permanent presence in the Alpha Quadrant. All this happens outside of Federation space so they have no rights to interfere as per the Prime Directive.
But do they leave the Cardassians to run their civilisation as they see fit? Of course not. They mine the wormhole which starts the war.
So as far as the Dominion War goes, the Federation were the clear aggressors. And let’s not get into the attempted genocide of the Founders.
The Prime Directive is about not interfering with the natural evolution of non-spacefaring civilisations. It aims to not introduce advanced technology in less developed civilisations before they are prepared to handle it.
It absolutely does not apply to either Cardassia or the Dominion, especially given they’re already establishing such presence precisely to fight against the Federation.
Other than that I kind of agree with the rest of your post. Though personally I don’t consider Discovery canon so I’d discard that. I know a lot of people feel otherwise and they’re welcome to do so but I have no intention of debating this.
It applies to every non-Federation civilisation. Part of it does include not interfering with pre-warp planets but that’s just part of it.
“Starfleet crew will obey the following with any civilization that has not achieved a commensurate level of technological and/or societal development as described in Appendix 1.”
Man, you didn't read past the part of the article you linked that "proved" your point, did you?
Section 2:
If said species has achieved the commensurate level of technological and/or societal development as described in Appendix 1, or has been exposed to the concepts listed in section 1, no Starfleet crew person will engage with said society or species without first gathering extensive information on the specific traditions, laws, and culture of that species civilization. Then Starfleet crew will obey the following.
a) If engaged with diplomatic relations with said culture, will stay within the confines of said culture's restrictions.
b) No interference with the social development of said planet
I'm pretty sure they quote the prime directive when choosing not to directly interfere with the Klingon Civil War. There's a specific emphasis on proving the Romulans are behind it before taking direct action to help.
I'm not going to say that specific depictions haven't emphasized that it's solely about pre-warp civilizations, but it's clearly used on at least one and probably multiple occasions to refer to post-warp interference as well.