Why no fast zooms for mirrorless?

In theory the size of the lens is proportional to the 3rd power of the sensor size (side length), so if m4/3 has appr. 2 times smaller sensor, which has 4 times smaller area, then a 24-70 equivalent for m4/3 must be 1/8 the mass of the Canon/Nikon/Tamron 24-70 f/2.8.

Of course the motor and some things do not scale that good, but on the other side lack of the mirror (smaller back-focus distance) give advantages in optical design, such as avoiding of retrofocus construction.

At the moment I know only one 24-70 f/2.8 from Panasonic, which is extremely expensive and is not that good optically.

So instead of using advantages of mirrorless, manufacturers produce hills of dark sh*t, like 10x zooms f/4-5.6.

For God sake, my Olympus Pen1 is already using ISO one stop higher than it displays, 
with 14-42 f/3.5-5.6 it is useless in everywhere except a sunny day. In a white room with 2 big windows on a partly clowdy day I get ISO400-800 (which is 800-1600 in reality) and 1/30sec (the slowest for people portrait). Smallest "Fill Light" in post processing reveals horrifying noise.

Let's see what else can we get for a m4/3:

Panasonic Lumix G F4-5,6/ 45-200 mm
Panasonic Lumix G F4,0-5,6/ 100-300 mm
Olympus M.Zuiko Digital ED 40-150mm 1:4.0-5.6
Olympus M.Zuiko Digital ED 9-18mm 1:4.0-5.6
Olympus M.Zuiko Digital 75-300mm 1:4.8-6.7

Tamron and Sigma have also adapted theit f/4-5.6 zooms for m4/3.

There is no a single f/1.4 fix lens for m4/3.

As I thought in the beginning m4/3 system disadvantages are lack of shallow DoF, worse ISO performance, but instead we should have get advantages: smaller size, weight and price, but in reality it costs almost as much as a FF, some necessary lenses are not possible.

For example:
Oly 9-18 f/4-5.6 - 505 Euro vs.
Newly released Nikon AF-S Nikkor 18-35mm 1:3,5-4,5G ED - 730 Euro
or
Olympus M.Zuiko Digital ED 40-150mm 1:4.0-5.6 - 330 Euro vs.
Nikon AF-S Zoom-Nikkor 70-300mm 1:4,5-5,6G VR  - 450 Euro (with real VR, not useless in-body IS)
Tamron AF 70-300mm 4-5.6 Di SP VC  - 330 Euro

So I don't know for whom is m4/3 system now.

In comparison to prosumer P&S (Canon G, Panasonic LX, Oly XZ...) it's bigger sensor advantages are killed by dark lenses. It costs more, it is bigger.

In comparison to APS-C - worse IQ, same or higher price; smaller, but same weight; lack of good and cheap lenses. 

Maybe you know?