Oh, then I don't know. But it is pretty strange it didn't help because when throttle is enabled it is almost unbearably slow to upload anything so not sure how it could still overflow.
Also when thinking about it the Micro:bit 1 build it is pretty limited due to low RAM and flash memory. Can you just type
NRF.sendHIDReport on left side if this method is even present? if not then the keyboard stuff won't work anyway and you would need custom build of Espruino to enable it.
Having the micro:bit v2 would be much much better.