I'd agree with Steve, very hard to see how an average semi could take you much longer than 20 minutes, particularly with WFP.
But even done trad, the average semi should only be taking you 20 minutes at the most.
you may not average 3 an hour, but once you have started work on the house, and providing said average semi has approx 12 standard windows & doors or so, 20 minutes should see you finished comfortably.
With WFP, providing the house is straight forward, 15 minutes absolute tops.
On a regular, repeat clean, with WFP a house of this nature should take you no more than about 12 minutes to do.
I'm not talking about setting up and putting away, just the work itself should be completed without too much effort, easily under 15 minutes, and I mean really easily.
One of the ones I listed was a straight forward semi with easy access, 11 windows including 2 doors, on the south side the frames had oxidised, but I still did the job in 8 minutes (timed) and that also included setting up and packing away.
I think that perhaps you need to tag along with someone for a morning and see where you might perhaps be going wrong...
but it does need to be someone who is cleaning standard houses in under 15 minutes...
Ian