Dynamic Voltage and Frequency Scaling (DVFS) is a desirable feature. You're not getting a 60W CPU in a 13" form factor, but you can get a 28W CPU that will run at 28W indefinitely while also being able to temporarily boost to 60W when needed and thermally able to.

It's fine if I could get an ultra book that could sustain non boost performance. But even that is too much to ask for intel. I have't tested recently released AMD cpus to claim AMD also falls short.

AMD laptop chips are pretty decent: you can find laptops/ultrabooks for about $700 running on a Ryzen 7 4700U. Based on a vs comparison on CPU Monkey it looks like it gets about 80% of the performance of the M1, though only about 25-50% graphics. However, you have much better ram & storage options, all at a lower price, and the graphics are still 2x to 4x better than Intel's on board graphics.

You've been mislead if you think the 13" Macbooks run at full boost clock all the time.

It looks like the M1 does run all out all the time (maybe because it never turbos that much to begin with).

When plugged in, perhaps, but when on battery those slower cores are going to get used more.

No, if you run a heavy computational load on a battery powered Macbook Pro it runs all out on all cores. Lots of reviewers looking at this. Battery life is worse of course under heavy load but still incredible relative to x86 for identical tasks. Faster and less battery usage.