(I think you should be very skeptical of anyone who hypes AlphaProof without mentioning this - which is not to suggest that there's nothing there to hype)
Three days per problem is, by many standards, a 'reasonable' amount of time. However there are still unanswered questions, notably that 'three days' is not really meaningful in and of itself. How parallelized was the computation; what was the hardware capacity? And how optimized is AlphaProof for IMO-type problems (problems which, among other things, all have short solutions using elementary tools)? These are standard kinds of critical questions to ask.
> A speedup in the movement of the maths frontier would be worth many power stations
who is it 'worth' it to? And to what end? I can say with some confidence that many (likely most, albeit certainly not all) mathematicians do not want data centers and power stations to guzzle energy and do their math for them. It's largely a vision imposed from without by Silicon Valley and Google research teams. What do they want it for and why is it (at least for now) "worth" it to them?
Personally, I don't believe for a second that they want it for the good of the mathematical community. Of course, a few of their individual researchers might have their own personal and altruistic motivations; however I don't think this is so relevant.
No, in my experience the whole practical question is, can it be found automatically, or can it not be found automatically? Because there is an exponential search space that conventional automated methods will not be able to chew through, it either works, or it doesn't. AlphaProof shows that for some difficult IMO problems, it works.