Mercedes is one brand I've yet to own but expect to one day.
Let's face facts, at least according to me, which may not be worth much:
1. I know you are speaking of the E Class, a very fine vehicle indeed.
2. That said, the S Class is, and has been for many years, the de facto standard by which all other luxury cars are compared. The Mercedes ride is incredible. The way it smooths out the small road ripples, not to mention big ones, is bar none. The tech, which some are not enamored with, and of course different strokes for different folks, is above reproach. The safety features abound. It is an incredible statement of moving machinery.
3. My son just traded in his C Class on a 2021 GLE350. The interior is beautiful. The screen across the dash is unmatched in its clarity and changeability. The interior lighting is a thing to behold, with more options in colors than a box of Crayola. It is a beautiful place to spend time.
4. The Panamera is not a close comparison in comfort, ease of entry and exit, or room. And I owned one.
5. I see no reason for Porsche to compete with or even be compared against Mercedes sedans. Porsche is about driving involvement, about sport, about the excitement of driving.
6. I'm young enough (64) to still enjoy driving and sportiness of a vehicle. For that, Porsche trumps Mercedes, trumps BMW, including my M5 in every way. (I am not speaking of AMG vehicles.) The steering alone on my Cayenne makes me miss my M5 not one whit. It is a feeling of being in control, of feeling where and what the tires are doing, unlike the fake, non-feel of the M5 which steering was terrible. I call it the wanderer.
However, one day I will want that comfort, that incredible tech which rises above the rest, and I will not throw away my shot and will own an S Class. The new one is above reproach, with 3D dash, etc.