Red
Agreed I've successfully used them in RF races. Particularly tracks with longer pit lanes. Although that said, I guess race distance would be a factor as well on how frequently they are useful. Although I can envision scenarios where they could still be of use at the lower distances I don't race 25% or 50% very often.
But hards have been anything but junk over the summer for me, they've been a very useful tool. That may change over winter with temperatures dropping at most tracks but that's to be expected.
I assume when you say that hard tyres must be viable for all conditions, you are talking exclusively about racing formats.
You don't actually expect them to work on a cold winters day in Hungary do you?
Without going into much detail about how I do my strategy, I logged every winner's strategy from my league and I use hards quite often like Giorgio and Craigie said at tracks with long pit lanes