I reckon a washer on the end of a pole and a hose can be as quick as wfp if not quicker, especially using soap to break down the dirt quickly.
Think how you wash your car or wash the pots , you use a cloth and rinse on both, I would use a wfp but did plenty by hand when i was trad.
It looks like one of them jobs where you could get 95% of the dirt off in the first 15 minutes , but the quality is in the detail which takes the longest.
Some people would stop after 95% and think it was clean , the true proffesional would carry on for another 20 mins to make sure it was 100% clean.
Remember one persons "clean" is another persons "dirty", so you cant really compare times.
Dave