The only two Mercedes I've owned were an SL500 and an SL55 AMG, which were 2-seater roadsters. They didn't handle as well as the Lucid, their rides were harsher, and the body stiffness was noticeably lower than the Lucid's. However, being roadsters, their lower torsional stiffness was to be expected.
I don't remember ever driving an S-Class, but I've spent a lot of time in the backseats of them, as they were our company transport cars.
The only thing I found better than our Lucid in my limited exposure to Mercedes was the rear seating position of the S Class due to its deep footwells. The Lucid with the larger battery pack has the same jacked-up knee position that plagues the Model S as well (although the Lucid has vastly more fore-aft legroom than the Tesla and is at least on a par with the S Class). However, I've sat in the backseat of a Lucid with the smaller battery pack, and it was every bit as commodious as a Mercedes S Class in all directions.
My other observation is that the SL55 AMG was second only to a 1998 Corvette in the number of mechanical failures it had. The car was in the shop almost monthly, including for things as serious as brake failures. Despite our Lucid being an early-build car, it has thus far proved far less plagued with issues than the Mercedes.