I agree.
I ran BOINC and other projects on a laptop for about 2 years.
The maths projects almost all ran the CPU hotter than other projects.
Primegrid was no exception.

1st thing is to prop-up the back of the laptop about 2 centimeters (1/2 inch) above the surface of the desk.
Most laptops use intake vents that are underneath the laptop.
Improving the air circulation underneath almost always helps.

Also, if you have set the BOINC project to use 30% of your CPU by changing your BOINC general settings 'Processor Usage' > 'Use at most' then you may find that it is using 100% cpu availability 30% of the time and 0% for 70% of the rest of the time.

That setting used to work for some projects and not others when I tested.
I have not re-tested again lately.
Perhaps you can tell us what your observations are in the Task Manager now.
(it really should not be running that hot otherwise)