They got there by skimping on IO

Please elaborate. IO is really not an issue in the M* machines I‘ve used - on the contrary.

none of the M1 laptops let you use multiple external monitors and all of the M1 products have much lower limits on storage than PCs.

Not true. Depending upon the processor choice, M1, M1 pro, or M1 max, you get 1, 2, or 4 external monitors. Up to 64 GB ram. Do you really need more than 64 GB? The number of users who actually need more are a very small part of the market.

And the M1 Ultra even offers up to 128 GB RAM -- and that is also unified with GPU RAM.

The price of RAM is absolutely bonkers though. If i ever need more than 16GB of RAM and more than 512GB of storage, I'll strongly consider moving back to Thinkpads or something.

There is a trade-off between the three kinds of improvements. It is possible to pick some points (for example) that give a less than maximum power reduction as well as a less than maximum speed improvment. I think the comparison would be the Apple Silicon that they released is larger than a (hypothetical) alternative that only improved performance but kept the other two constant.

Maybe X*Y*Z=K but K increases over time. Ten years ago, we couldn't do what we can do now.