I copied a keyboard's directory "/keyboards/handwired/108key_trackpoint" and used it as a template for my handwired keyboard.

I don't have a PS/2 trackpoint, so in rules.mk I set:

PS2_MOUSE_ENABLE = no
PS2_USE_USART = no

under the comments that say "change yes to no to disable"

When I looked at the matrix debug, though, I eventually got a bunch of PS2 errors, which were probably tying up the CPU, causing my original problem of extreme lag, and missed keypresses.

after instead commenting out the line, it works correctly.

It looks like the code just checks if they're defined, and not if they're set to no.