OK, I really don’t have the time to wade through this entire conversation, but TL;DR no, this was not delivered as promised (or rather as advertised).
But before I explain why, I want to make it clear that I love this game as much as you do. It stands head & shoulders above X-Com and all of its clones, because of its open sandboxy nature and the AP/targeting system. It has effectively retired all those other games for me until someone like Firaxis comes along and adds some much-needed balance to the design while they steal the best bits of this game.
But what was advertised, what I bought into in the Fig campaign way back when, was a TBS with an enemy that - and I quote - “evolves new forms in response you your tactics!” Wow! Now that’s what I’ve been waiting for all these years. THAT, right there, is the Holy Grail. THAT I can get behind 
You see, much as I love them, the problem with every TBS I’ve ever played is the Inverse Difficulty Curve, where you start out struggling to survive, but by the endgame you’re so powerful that you can virtually stroll blindfold through most encounters without breaking a sweat. XCOM almost fixed it for me with a combo of the Long Wars and the ability to switch Difficulty mid-way through a game. So I’d start on Veteran and every time I hit the big ‘turning point’ missions in the storyline (the Advent Body Factory or the Alien Flagship) I’d turn the Difficulty up a notch. It was still too easy by the end, but at least it provided a modicum of challenge.
What PP promised (and almost delivered) was an enemy which responded to the way we fought - which did what real enemies do in (especially modern) warfare, by looking at what we did and changing its systems to deal with that. So just like tanks were a response to machineguns dominating the battlefield and anti-tank guns were a response to tanks, I expected the Pandas to evolve bigger shields in response to my snipers, ablative armour (which takes half damage to explosives) in response to my Boom Blasting Heavies, and massively innacurate armour-shredding weapons in response to my blatant abuse (dare I say it: ‘exploitation’) of vehicles.
We never got that. We still don’t have it. The closest PP got to it was the Dynamic Difficulty Algorithm which simply added extra enemies to each mission if you were doing well and subtracted them if you were doing badly. Only problem was, that took no account of the way many modern gamers play their games today by - for want of a less emotive term - Save Scumming. So if you saved and restarted till you got a perfect score, the game treated you like a gaming god and hammered you for it - cos how was it to know that you were massaging your ability score by only cherry-picking the best outcomes? People hated it. Some argued (erroneousy imho) that it ‘punished good play’ - which it didn’t: it punished bad play that pretended it was good. But it got junked because casual gamers simply couldn’t cope with it.
Good players - or rather players who got the ‘meta’ - had a different complaint. Because the meta is such that unless you play with a host of self-restrictions (which in my case runs to more than a page: What Self-Restrictions do you Use?), it is perfectly possible for a single squaddie to completely break the game by, for instance, strolling through the first chamber of the Final Mission annihilating every Panda there - including 2 Scyllas - in the first turn of the mission! So rather than fixing the Inverse Difficulty Curve, PP’s biggest strength - its open sandbox system - has exacerbated it by failing to add any colldowns or other limitiations to the stupidly OP skill combos you can simply stumble on by accident in this game.
Now, I’ve seen you argue elsewhere that the devs are perfectly within their rights to shut down an ‘exploit’ when they find it - and that’s what they’re doing. Some players hate it, but you are no longer able to pump 15 Sniper rounds into a Scylla with pinpoint accuracy from the other side of the map by abusing Rage Burst in a way that was never intended - and I for one think that’s a good thing.
On the other side of that coin, I have been a ceaseless voice calling for Easy Difficulty to be just that - easy (which it still isn’t imho). But I also want Heroic & Legendary to actually require you to play like a Heroic Legend to beat it - which it doesn’t.
Proper Reactive Evolution would go some way towards solving that. PP’s already halfway there with the Evolution System they have in place. Now all it needs is for the devs to use the much-vaunted analytics they used to eg. nerf Piranhas because they were being overused, to say: “This team uses Snipers 70% or the time, so let’s evolve a Hoplite-style Tower Shield for the Pandas to counter that; this Teminator Build is abusing Dash & Rapid Clearance, so let’s evolve Goo-spitters or motion-sensitive Reactive Firers to make Dashing into the open and shoving a shotgun at point-blank range into a machinegun-toting Panda’s face the kind of stupidly dangerous action it ought to be.” And so on.
TBH, I wouldn’t even mind if it was a Second Wave Option. I’m all for players being able to play this game the way they want to play this game. But that stands just as much for the so-called ‘hardcore’ as it does for the more casual player. I want a casual player to be able to breeze through this game committing Terminator-style mass-murder with ridiculously untactical suicide-charges as much as I personally want the Pandas to evolve ways to show me just how terminally stupid such behaviour should be in what purports to be a ‘Turn-Based Strategy & Tactics’ game.
But right now, because ‘Reactive Evolution’ is nowhere near what was promised in the Fig campaign, I have to treat this game like it’s a 5-year-old and play with one arm tied behind my back. And I have beein doing so almost non-stop for the past 2 years because even with all its mind-bogglingly irritating foibles, this game still stands head-and-shoulders above every other TBS I’ve tried.
I just wish I didn’t have to, is all.