It may be easier to add diodes on the coils themselves. No extra wire, no connectors which may fail, just solder 4 diodes on the 4 coils.

This is the eye of the beholder.

Diodes on coils are supposed to be as near as possible to the source of the voltage spike. Theoretically.
Practically the 2m. wiring is not a long distance at all, so it really doesn't matter if it is on the PCB or the coil.
When a coil is replaced and the wiring is connected wrong... results in damage.
So from that point of view it is best to put them on the driver board.

However: when this system (the 8-driver board) depends on a very thin wire which is connected to a coil, and if this wire breaks it results in burnt coils? I think that can be seen as a design flaw. Especially when connected to the playfield, with movement, vibration, solder-connections, etc. one can expect that wire breaks are possible.

And the design for the 8-driver PCB is imho also flawed on the data lines through the flatcable: it results in burnt coils or flashers burning plastics when the flatcable is old. A simple resistor array can be used for a better (very cheap) solution, but this is not the way de PCB is designed.

Again: this is in the eye of the beholder...