I agree that psykers can be crazy powerful. So much so that they throw the balance of power for their XP level? Maybe, but I think that's a discusion best suited for a more narrowly focused thread...
And can we drop the argument that everyone can recognize an unarmoured CSM? A) 99.99% of Imperial society has never seen an Astartes or CSM before and would have no frame of reference, and B) Take a look at the members of House Goliath in Necromunda for an example of the ethnic diversity produced within the million worlds of the Imperium- they look exactly like unarmoured CSMs! Add to that the genetically-manipulated, surgically-altered bodyguards of the wealthy elite, and it's absurd to think that every hab-prol catching a glimpse of an unarmoured CSM will start yelling for the Inquisition!
On combat: yes, the guys with the heavy weapons will generally target the greatest threat. Usually, that will be the CSM; but what if line-of-sight is blocked, or what if the CSM is engaged in melee with his back to the guy with the krak missles, but the Renegade is clearly targeting him with his plasma gun? Does the game require the heavy hitters to treat the non-CSMs as invisible?
And I just don't buy the argument that intelligent tactics will garantee the survival of Mortal PCs- that assumes that they are never surprised, that enemies never use Blast weapons, that combat never takes place in locations without lots of cover, etc...
But like I said, I could be wrong. I'm still waiting to hear some detailed descriptions of combat from people who have actually played a signifigant number of games.