Bugzilla

For whatever reason, on retesting both the games, i am getting 2.3s on each taskcontroller thread on the same builds as in OP.

Edit:  I found that choosing the Device Manufacturers Power Setting has a big impact here.
On "Balnced/Optimized" Default Lenovo plan : https://share.firefox.dev/4j6y22h  (3s)
"High performance" Lenovo plan: https://share.firefox.dev/4aaRRBu (2.3s)

Note that this power setting is outside of Windows control panel. 

Maybe whenever WASM is compiling parallel threads,  consider temporarily increasing the power setting (either the Windows power setting, or the device manufactureres setting.)