Well we'll see in the long run how this shakes out. I dunno if it has indeed had the shit softened out of it. Everyone who's driven it say its more than the sum of its parts when it comes to driving dynamics, despite sharing the same platform as the SL.
And sharing the same platform is meaningless, because the C, E, S and their GL variants all use the same platform too.
I agree with the price being wrong for this type of car, but if the people who have driven it like the way it drives and feels, and more people buy it, then mission accomplished.
That remains to be seen. The SL43 is about 230kg (446lbs) lighter than the SL63. Part of that will be the smaller, lighter engine, but the AWD drivetrain will also impact things. The M177 is apparently 209kg, where the M139 is 160kg - so around about 190kg (400lbs ish) can probably saved with the transmission alone, which is not insignificant.
They can also fit a transaxle to it, and make a 2-seater only variant if they want. They can add carbon fibre pieces here and there and everywhere to reduce weight. Of course it won't be as light as a GT Black (probably), but they definitely can strip out a lot of weight if they wanted to.
Also, I'm fairly sure that the 911 GT3 RS is slower to 60 than a Turbo S, but that doesn't mean its any less desirable as a car. There is a reason there are about a billion variants of 911s - and that's cause each of them serve a different segment of the market.
Whether or not AMG will be anywhere near as successful as Porsche in this segment off the back of this GT remains to be seen.