Picard *outright told the Cardassians* that he knew full well Maxwell was telling the truth all along, but had chosen to preserve the peace talks by refusing to look at the factual evidence and pretending it didn’t exist. He tried to say he’d hold that over their heads as a deterrent against further attacks, but the Cardassians correctly pointed out that this was an empty threat because he had proven himself to be too much of a coward to actually go through with it
Okay I think you're memory of the episode is a little off. For starters the episode starts by confirming that "It has been nearly a year since a peace treaty ended the long conflict between the Federation and Cardassia." There are no "peace talks" since the War is long over by this point in time.
Second the episode ends with Picard's "We'll be watching" warning with Gul Macet not offering any rebuttal or claiming it was an empty threat.
Nor would I classify Picard's action being motivated by cowardice. Rather if anything it seemed to stem from a holier than thou attitude and complacency on Picard's part. The Cardassians were not a threat. From the Federation perspective it's unclear if they were even at war at all in the first couple of seasons of TNG are to be of any judge. Starfleet is happily and merrily exploring space peacefully despite technically being at war with the Cardassians until the 3rd season.
So the fact they were re-arming was of far less importance than the fact Maxwell had violated the treaty. Not a mindset I agree with but one I can understand. Through even with their honor before reason, Picard still said this about Maxwell:
The loyalty you would so quickly dismiss does not come easily to my people, Gul Macet. You have much to learn about us. Benjamin Maxwell earned the loyalty of those who served with him. You know, in war, he was twice honoured with the Federation's highest citation for courage and valour. And if he could not find a role for himself in peace, we can pity him, but we shall not dismiss him.
One could certainly complain that Picard has his smug head up his ass in the episode, I certainly have in the past, but nothing indicates he's trying to frame or belittle Maxwell or seeks anything but for Maxwell to answer for his actions.
And I will point out that Maxwell and his crew should have exactly the same information regarding the location of the "research station" and cargo ships running to it with jamming fields that Picard mentions. So even if Picard desired to withhold this information it would still be brought up during any trial.
Which ties back to Picard's warning. The Federation will now know the Cardassians are re-arming and will be watching them accordingly.
And basically appeasing the Cardassians while they were winning and while the Cardies were invading planets where federation citizens lived without any proper claim to them is what?
That the Federation decided some insignificant colonies on the edges of their territory weren't worth the cost of time and lives lost to keep them, both in Federation and Cardassian lives, and which their enemy had at least some basis for a claim is, if anything, proof of competent leadership rather than the inverse.
The Federation knew what it wanted and what it would be willing to pay to obtain it and did so. While a bit of a dick move to the colonists in those planets by all accounts they could make new homes elsewhere and in at least some cases those affected were granted some kind of Cardassian citizenship that allowed them to stay on their world of choice.
And I'm surprised you cling to this conflict, a rather minor one from the Federation perspective, as opposed to the Dominion war
Yes, they are soft, often self-possessed, troglodytes that will become instant Slaanesh chow.
I would have to disagree. As you yourself bring up, Slaanesh isn't the God of pleasure or love but ultimately of excess. And that is something that the Federation isn't. And we know from Barclay that there are social pressures against those who start to develop holo-addiction and whose fantasies were so mild I'm not even sure Slaanesh could count them.
And before any of that could happen there would need to be a point of contamination. A cult member, rogue pysker, artifact ect which brings the unfortunate soul in contact to Chaos.
Additionally your argument rests on the presumption that the Imperium society is ideal or at least effective at curbing Chaos influence which does not seem to be the case. To quote from the rule book:
Not all heretics are mutants, however. Amidst the grinding misery of the dystopian Imperium there are countless reasons that a Human soul might turn to the worship of Chaos. Some seek release from lives of slavery, poverty and hopeless, endless toil. Others desire power or influence, whether to prove for those who depend upon them or to revenge themselves upon those who have oppressed or mistreated them.
Core Rule book, 2020, page 36
Simply put the Imperium causes as much of the problem as it solves with its brutality. In comparison the utopian Federation gives far fewer reasons to want to join up with the Dark Gods.