Tread depth is an interesting part of it as said. How the tyre behaves as they wear over the last part of it's life is equally important as the start, and IMO is why nobody should form an opinion of a tyre until they are worn out.
My theory as to why, trailing arm suspension on the back works quite differently to mcphearson strut suspension on the front, camber seems to deflect a lot more on the front than the back because of these two designs. Add in the job of steering on the front only, and power driving the rear only, all conspire to wear the tyres in very different ways. Fronts loose the edges first and give a rounder profile, where as rears wear the middles flat as if over inflated giving the exact opposite profile.
Why is this relevant to tyre choice? Not all tyres behave the same under such wear, some handle it better than others possibly due to construction. And has been a major lesson learned in my much bemoaned Falken disaster. When new they where ok in the stability dept, not good, but merely ok! Still thought the wishbone bushes where buggered tbh but they point is they are a less stable tyre generally.
So add in the tyre wear characteristics of the car previously mentioned, in my case Elite suspension which is soft which will allow camber angles to deflect even more exaggerating that wear difference front to back, and an enthusiastic driving style pushing the suspension movement and hence camber deflection further still, and the end result for a tyre can mean binning them with 3 or 4 mill of tread left as the car simply will not go in a straight line.
Don't get me wrong falkens are not the only tyres to reach their level of poor handling(comparatively speaking of course), ask TB after his " something's broken, as if disconnected" concerns before changing tyres and the problem vanished. The point is at what stage do they reach this unusable level and they just have to be changed because they bother drives so badly?
From my experience, I would suggest, once again, the tyre wear and resulting handling degradation to be totally unacceptable on Falkens ESP the 912... But then I really should say similar of the suspension as well, and admit, bought the wrong tyre. 
I don't normally take my tyres down to the legal limit, but the lack of availability of my beloved SP9000 and trouble making up my mind in finding a suitable successor, meant it happened.
You drove it after rear bushes were done, and again when 'something was broken' episode, and the tyres had fallen off a cliff. Suddenly. Fortunately, your experience with the Falkens that I refused to drive after a couple of miles at Asheridge, you were able to say it was just the tyres had exceeded a certain point in their life.
I believe you and I don't have dissimilar driving styles most of the time, so as you rightly say, a tyre that suits us is unlikely to suit people like tunnie, for example. I must say, I *really* hate those michelin on the Elite, they are bloody awful from a grip point of view, but I am sure that a Sunday afternoon old duffer would love them? Though, no matter how spirited your style is, surely the one thing you must have from a tyre is grip?