Firstly, I'll hedge by saying I'm highly unconfident in my own, or anyone's, ability to foresee how this turns out in the long term (say, twenty or fifty years).
On creating fewer jobs:
Earlier automating technologies didn't grind to a halt, or stop economic growth, because they put everyone out of a job and thus noone could afford them.
If you think AI will, you need a story for why it may be radically different this time.
I think AI might be radically different, though I doubt it will be so in a way that makes it all peter out.
On AI valuations: I think AI is possibly in a local bubble (as in, we may be going wrong in predicting which firms or assets will hold long term value, and/or there will be a sharp correction along the way).
My personal best guess is that long-term, AI is not a bubble at all, and may well be massively undervalued.
People are very bad at predicting exponentials (think of Covid), but AI is becoming more capable exponentially. It is also being adopted more, although overall, AI usage remains low compared to where it could be (think of, say, how many people use the internet now, compared to in the early years).
Unclear what a 40% crash would do. Certainly not pretty, though a lot of AI funding is via private credit (which implies its own problems).
But if the technology is here to stay, data centres will be needed.
I think ultimately they will migrate to wherever can give them a good balance of cheap energy + stable politics. I'd like that to be the UK.
That means lots more nuclear (and other) power. Luckily, investing massively in energy won't be wasted regardless, because we are already so badly lacking.
If we can build the network effects then we may get to keep more of the industry than we 'deserve' on those grounds. Currently we do have quite a lot of AI (probably the biggest frontier AI talent pool outside of California), so it's a matter of keeping it and growing it.
There is no contradiction at all between doing that and regulating/governing carefully. Indeed, having a decent AI sector is the only way we can effectively govern it.