The way I see it, it's clear that human-level intelligence can be achieved with hardware that's toaster-sized and consumes 100 watts, as demonstrated by our brains. Obviously there is some minimum requirements and limitations, but they aren't huge, there are no physical or info-theoretical limits that superhuman intelligence must require a megawatt-sized compute cluster and all the data on the internet (which obviously no human could ever see).

The only reason why currently it takes far, far more computing power is that we have no idea how to build effective intelligence, and we're taking lots of brute force shortcuts because we don't really understand how the emergent capabilities emerge as we just throw a bunch of matrix multiplication at huge data and hope for the best. Now if some artificial agent becomes powerful enough to understand how it works and is capable of improving that (and that's a BIG "if", I'm not saying that it's certain or even likely, but I am asserting that it's possible) then we have to assume that it might be capable of doing superhuman intelligence with a quite modest compute budget - e.g. something that can be rented on the cloud with a million dollars (for example, by getting a donation from a "benefactor" or getting some crypto through a single ransomware extortion case), which is certainly below the level which would draw attention. Perhaps it's unlikely, but it is plausible, and that is dangerous enough to be a risk worth considering even if it's unlikely.