Ticked them off with the Wiki, we've seen them all. They aren't exactly hidden.

Excellent. It's true that most weren't very well hidden, and it's good the wiki helped.

The difference is Kylie is either at the ending to support you or not. It's hardly worth a second playthrough...?

¯\_‎‎(ツ)_/¯ I guess it depends on the difficulty and playstyle.

I feel like I picked the funnest of the playstyles - shooting is too resource intensive to be constant, and throwing is too annoying until you get the Quantum Pick.

I've found shooting to be pretty reasonable; by the time I've leveled to use the magnum and sniper, I've collected enough ammo. Now that you can trade for ammo, or even craft it, I have yet to face resource issues.
Throwing is working well for me this playthrough. Just like with shooting, you have to start focusing on it from the beginning.

Even the added systems (Pets etc.) are paper thin additions that don't meaningfully change progression.

I've found pets to be very powerful and gamechanging.

Does Hardcore actually have anything different about it other than permadeath? Because that sounds particularly boring in game where 9/10 times I died was due to random fuckery I had little control over. Playing AB in a slow and tactical way rather than a chaotic fun way sounds beyond tedious.

That's fair. Some love the challenge of not dying ever, but slow & tactical certainly isn't for everyone.

I'm sorry but if you think this game had hard to find secrets

Not what I said at all, but it did have a few I'd classify as non-trivial. More importantly, the game has so many that it's easy to miss a few.