Its not that heavy. The packing weight info from bmw is not correct.
I'll measure the exact weight when its on the lift again and we'll see how far you're off.
It can be lightened by ~700gram by removing the anti resonance weights. See the german forum for extensive info on this mod.
But it will be heavier than the AP caliper because, as I said, the pad in the BMW/Brembo caliper is considerably larger than the pad in the CP5575, both in lenght as in width. Because the width is also slightly larger, the overall disc diameter can be smaller to achieve the same disc area resulting in a smaller rotational inertia of the disc.
I havent had any of these problems but then again, its a combination of pads, fluids and discs. Maybe you had an unfortunate combination. And on the german forum no one experiences these problems, so I think this is more an individual problem than a general problem. Anyway if desired the pistons can be changed to stainless very easily from suppliers like RB (the piston diameters are fairly standard, so also silicone seals are available)The caliper definitely has problems with dispersing heat, under very hard use (lines, fluid and pads all the same in both of my kits) the difference in feel between the bmwp and ap kit is very noticeable. After some hard lapping the pedal loses feel and it is not hard to make them fade, on the north loop I expect they'd be ok, on the gp circuit not so much.
It is proven that calipers made from 1 piece with fixed halves and a fixed bridge is way way stiffer. Look at formula 1 were costs and manufacture difficulties play absolutely no part: NO caliper is made up of 1 bolted halves. they're all one piece.
Swapping pads on a 1 piece caliper is not that much of a pain as you make it seem to be.
First you have to remove the wheel: thats 5 bolts. You have to do that either way (jacking up the car etc etc)
Getting the caliper off is an extra 2 bolts. Thats all and you can get the pads out.
I dont think 2 extra bolts is that much of a problem? (actually the bridge of a 2 part caliper is also bolted so its hardly any extra work....)
The maximum thickness for the discs is I think about 30mm. Sure a bigger caliper can use thicker discs, but do you really want all that extra unsprung extra rotational weight? on a 1300kg car?
The /m discs are very very well race proven. Even professional race classes with z4's have used them. (again see the german z forum, there's a professional racing driver active there from the schmickler racing team, having raced z4's, on occasion even with the stock brakes, if the track allowed it: again: less rotational weight is better).
). But that is an individual choice, I've seen these weights also on the more exotic ferraris like stradales etc (equipped with brembo gt above brake systems 
), so apparantly this is an accepted way of doing things, trading less unsprung weight for more stability. But those weights are all removable, so its a choice.
)
). That's why they're cheap.