The 5DM2 is superior with FAST LENS. Its common sense. Fast Lens ...More light. I call it cheating but ....
It's really much more complicated than that. I've been doing a LOT of cross testing and there is much more to it than 'use a fast lens' or don't use the 'kit lens'. Fast lens or not, the 5D2 and 7D still need elevated ISO settings (e.g. ISO 1250) to match the exposure levels the HMC can achieve when the IRIS is open.
If you are using 'fast glass' (e.g. 1.2, 1.4 etc) then you have other problems to deal with, like depth of field / focusing challenges on the 5D2/7D that you simply don't have on the HMC. OTOH, if shallow DOf is what you are looking for then the HMC simply can't achieve it.
If you are looking for 'wide' and 'up close' and shallow(ish) then the 5D2 is the clear winner with the 7D very close behind. However, once you get past the 135mm range (which I shoot a lot of) the 5D2 and 7D's advantage are not quite so clear, especially if you need more than a couple of feet of DOF. There are times when shallow DOF just won't work because things (people) are moving too fast for you to keep rack focusing with the required accuracy.
.....fact is fact. Now if you but the kit lens up with the HMC150 then of course the 5DM2 is going to have problems and have to up the ISO.
'Fact is fact' is an interesting way of looking at things. It depends on what 'facts' you are considering and what you intend shooting. The example video posted by RenewableEnergyNews would have been useless if 95% of the property had been out of focus due to shallow DOF.
There is much more to consider than simply using a fast lens.