On the one hand, I think it has always been a bit like that. Valuations have probably always felt a bit crazy to some people, if you look at the long term charts they are always high by historic standards. Debt has been high for generations, certainly since the world wars - the debt raised to pay for WW1 was only fully repaid a few years ago. There has always been layering of debt upon debt. If you are wrong and things carry on as normal, debt and stock market valuations will be unimaginably high and today's levels will look modest, the way the levels from the 60s and 70s look modest now.
Having said all that I do get the same feeling you do. QE is a bit of a game changer, it has accelerated things. And even bankers regularly use the "addiction" metaphor when they talk about the impact it has had on the financial system - an interesting advance on the "life support" metaphor they tended to use straight after the crisis. You can see why they do. The financial system is like a person who had a bad injury, took a load of pain killers and is now a heroin addict. The fact we have these "taper tantrums" every time people think rates might start to go up really is a problem. It suggests the debt levels may now actually be unsustainable if people have to actually pay to service it. Everybody accepts the stock market is where it is because QE money has been pumped straight into it.
So yeah, I do see where you are coming from. Im torn between worrying the whole thing is a house of cards on the one hand, but having complete confidence that banks and central banks will do whatever it takes to keep the show on the road on the other. If we didnt solve the problems from 2007-08, but just kicked them down the road, it will be really interesting to see if governments actually have it in them to respond again. If QE stops working I dont know what they do next. But for sure there are some creative economic minds out there, Im sure someone will have an idea.