Then why not present such evidence to Picard on his arrival? Most things point to the fact that Maxwell had no concrete data to back his claim, even though it was correct. Even the original script reflected that a bit more. Maxwell is mostly just saying things seen & heard, & the strategic implications of said things, are enough for someone in the field to understand the situation, even if they can't fully report it well enough to get support from HQ.
If he truly is an exceptional captain, like O'Brien says, then he probably did report some stuff he saw & heard, & it got passed over by the big wigs, because they don't want another conflict, but Maxwell being who he is, with what's happened to him, could not let it rest.
I can't imagine HQ had much more to go on when they sent Picard in to investigate those stupid Krieger waves. Frankly, Starfleet is just plain gullible about Cardassians. They'll let them run around arming bases in sensitive areas, because "Not enough evidence" but then are willing to breach borders to deal with a threat, upon which they clearly had very little evidence, as it turned out to be nothing but a trap.
Honestly, Picard is being a little gullible with Maxwell's Cardies too, even if that's mostly because he's under orders to keep the peace. Heck, it was pretty blind of him to not offer up an argument about going into Celtirs III, if you ask me. I can't help but think the only guy in Starfleet who knows wtf to do with Cardassians is Jellico... & Maybe Sisko
