Plumbing code requires at LEAST 1/4"/foot...nothing you do now will correct that other than a tearout IMHO.
Actually tearing out the mudbed would be pretty fast and easy in the scheme of things. Then, you'd have a choice of either using the conversion drain or tear the drain out and use the regular Kerdi drain, which is a little less expensive. You wouldn't need to tear out the curb or bench though as long as they were installed with adequate pitch and are stable.
Even with the divot method, you'd still need adequate pitch to the drain first. Note, Kerdi works just fine over either their foam pan or a mudbed. Materials wise, the mudbed is more flexible and cheaper. Labor, a competent installer should be able to get the old mudbed out and a new one in in much less than a day. It needs to rest (cure) at least overnight before you can install the Kerdi, and that needs a day before you can flood test (don't skip that part!), then, you can tile. In the interim, above where the flood test would go, they could start tiling the walls, if they wanted. Only the flood test needs things to rest first...the walls and bench could start tiling as soon as the Kerdi was installed.
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Jim DeBruycker
Not a pro, multiple Schluter Workshops (Schluterville and 2013 and 2014 at Schluter Headquarters), Mapei Training 2014, Laticrete Workshop 2014, Custom Building Products Workshop 2015, and Longtime Forum Participant.
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