I can’t say I’ve had any problems with wiper blades renewals, previous KIA car renewed at 2 years no questions asked and current VW renewed at 2 years and no problems. My other 3 Motability cars from years ago never needed there blades renewed, blades must have been more robust back then.
The VW was last Spring so don’t know if something has changed since then but MB are certainly scrutinising everything these days that sort of puts the “worry free motoring for the disabled” saying as nothing more than run of the mill advertising BS.