It can be done with zero timers too, in case the program has a superloop that has a reasonably stable iteration speed.

The bad thing with just counting number of turns through the superloop is that adding/changing code will change the performance - potentially enough that a user notices it. And an unbalanced superloop that runs differently fast in different modes can be very irritating if it makes a key auto-repeat change the repetition frequency or delay to the initial repetition too much.

That is a reason why the program really should make use of hardware-based timing for keyboard processing.

For some processors, other methods than timers may be used. Having hardware SPI, the time to send x bytes may be used. This method of timing can be used even if no external SPI hardware is connected. It may waste a couple of processor pins but that can sometimes be accepted. In the same way, a potentially unused UART can be used to supply timing if a suitable baudrate setting can be arranged. And many times, a timer used for other tasks may be polled to measure the length of each superloop iteration.