No, they limit the W...since the imac pro is working so great under full load without reaching 100C...
Mac Pro is a desktop with a humongous cooler. I can easily imagine that it can dissipate 300W+ of sustained CPU power. The heatsink alone looks like it would weight around a kilogram kg and have a surface area of a small hotel lobby. And it has 3 of what looks like 17cm fans.
If you want to run a Coffee Lake Xeon at max turbo frequency at 90C, you'd need more then 120Watts of cooling power dedicated to the CPU only. That is just not going to happen in a thin and light laptop. And as to runs cooler... the way Appel designs their laptops is that it allows them to draw as much power as they thermally handle. So it doesn't matter if your CPU is more power efficient — it just means that the MBP will allow it to draw more power (and thus run faster) at the same temperature. Its not a Dell who power-throttle the CPU (at least they used to, no idea if they still do). Apple primarily temperature-throttle.
But of course, we will see. Apple might move to power-throttling as well. Looks better on paper, customer gets less, but hey, if you know that you are being screwed over, you won't complain, right?