I actually had an epiphany while I was discussing the nerf with my Dad (no, he doesn't have any interest in TF2, he just tolerates me babbling), that the power of Demoman greatly changed the course of mapmaking in TF2.
That's because it always struck me with Valve's early maps that they were chokepointy and much smaller in comparison to modern versions - compare the stages of Goldrush to the stages of Thundermountain, for example - and my theory is that that change was forced by the disproportionate power of demomen.
When stickies were used to trap doorways and defend points, they weren't used for their damage dealing potential. When players discovered that stickies were much more effective than pipes in direct combat, they started to be used as such.
This meant a large amount of damage over a large explosion radius, so players wanted to spread out more. Valve had not previously accounted for this in map design, so to compensate, they did exactly that - making chokes and points larger to allow players to spread out to combat the threat of stickies.
Of course, larger areas means longer sightlines. Long sightlines need to be countered by a greater density of large props (which frequently looks ungainly) or greater height changes. This means more displacements. Note that Granary has almost no height variation. That's more realistic, but it doesn't help sightlines. That's why community 5cp maps today feature incredibly unrealistic steep hills, like the valleys throughout Process - to deal with the larger arenas, to deal with the longer sightlines.
Likewise, when we test maps in gamedays, one of the first things brought up in feedback is whether the map is too powerful for demomen. As map designers, we always write off the fault as something wrong with the level design. Maybe it's Valve's problem instead.
I feel like the "radius ramp up with time" version of the nerf that's been suggested in various places would be the best idea. Means demos with good aim/timing can still do great damage, but it's far less spammable.
My issue with that is exactly what I've been wrangling with the reduced radius of the Air Strike - it's infuriating when you don't get the kills you feel you should, because your gut tells you that the explosive covers a particular area. In fact, I suspect this is a problem that has no real solution under the current paradigm - Valve feels that the Stickybomb Launcher is too powerful in direct combat, but the competitive community (generalising here) likes the current stickies exactly for that reason. Any nerf would be a nerf too far. As Valve said: "We will continue to evaluate the use of stickybomb air detonations and potential changes to that mechanic." It's not about the strength of the nerf they gave us. It's about reconciling what they want the Demoman to be about and what it has grown to be.
