Yes, I think there is a lot of misconceptions going around takeoff techniques and how they relate to the figures in the POH.
The POH figure is for a dry hard runway, unless otherwise stated.
A "soft field" takeoff is going to use a lot more runway than the hard runway figure. Even doing a soft field takeoff on a
hard runway (pointless except when doing an FAA checkride perhaps) will use a lot more runway because of the extra elevator drag, acting like a giant air brake.
I suppose that in a low powered type (e.g. a C150) a soft field takeoff may be the only way to get off the ground so one cannot even do a comparison with a normal takeoff off the same muddy grass, but the resulting takeoff run is going to bear little resemblance to what is in the POH
I did a soft field takeoff the other day in the TB20, off a hard runway, and the run, including the bit in the ground effect, was about 600m. Whereas a normal takeoff is about 350m, both cases about 10% below MTOW. It was staggering how much extra drag there is due to the elevator being all the way back. A soft field takeoff may keep the mud collection down but that's not much use if you don't get off the runway. And this is a TB20 which has loads of power.
Those flyers that get handed out about grass taking 30% more than tarmac, etc, are meaningless in so many cases, IMHO.