Not loading the shaft a lot is your key, smooth doesn’t need as much stability and I do think the newer shafts tend to hold shape better, so I could see a lot of people being able to move down from their old standards. I have tried a few times, just like Weirfan, I get balloons. I have to really back out to make it work and that’s just not my game, at all.
Now, I will say, there was a time when I was buying X flex shafts and tipping 2 inches to control the flight and that’s no longer necessary, but some of that is from a reduction of violence in my swing and less club head speed, but the other part may well be just plain ole better shaft technology. If I had it to do over again, I would have tipped my current driver shaft a hair more.