The reason the kernel takes a while is because of all the drivers it has to load.
Basic kernel 101 here:
Kernel’s are the foot print that communicates system devices with the software layer of the OS.
With this, especially so in Linux, some systems don’t care what has to be loaded to boot, others care very much, as is the case with your laptops here.
The reason it takes a while is because it’s loading the kernel and loading all the drivers in the system. Then the kernel checks the system for what it needs. If you where to have debug displayed, you’d likely see things failing all over the place as the driver being loaded doesn’t exist or is unusable on a particular system.
I can’t tell you WHY it’s fast on some and slow on the others. Just understand this is the case.