Defender washers actually work perfectly fine so anything less than a decent squirt of water onto the screen regardless of speed means you have a problem that need to be sorted, just saying " Defender washers are useless" and ignoring it is a cop out.
Blocked / kinked pipe is possible as is clogged motor or defective nozzle.
Access to the nozzles is dead easy by removing the dashboard top-rail, shouldn't take more than 10-minutes at most. If you have the early single-jet nozzles then consider replacing them with a pair of the later twin-jet nozzles as this will double the amount of water hitting the screen and the standard pump will cope just fine. If you have a single twin-jet nozzle in the centre of the bulkhead then the holes exist to allow you to fit a pair of them, one each side. I did this conversion to my 90 12-years ago and it is really effective.