I am using slackware64-current and I have tried kernels 6.1.60, 6.6.6 and 6.6.20 (huge kernels), with elilo.
With versions 5 and 6.6.6 messages during boot process appear almost immediately. With 6.1.60 and 6.6.20 they appear after 5 or 6s. But the boot process takes the same time for all kernels.
Why ?

Another old problem with all kernels 6: I launch KDE from console with the command 'startx'. But it it impossible to come back to the console. I get a black screen with unresponsive keyboard ans mouse. It is still possible to halt the system from KDE.

Does it matter? I don't think so. As for your console problems, you may not have set up your console environment properly, so things have no drivers. The keyboard should work, but the mouse needs gpm.