I can understand many of the points you make here. To respond to the section on myself.
I have always played the RPGs and Play by post is new to me however I would be very hesitant to suggest that being big and slow is a great trade off for roughly eight or nine points of armor. The frequency of weapons that would laugh their way through that is quite high and the bulk makes the far superior dodge unlikely. A GM that cannot bring down a Malek is not nearly imaginative enough. I have full confidence that i will spend more than enough time in the repair bay.
Which also brings me to another point you touched on. Demons. I'm always skeptical of any mention of characters facing off against them one on one and winning. They are absolute combat monsters. Even lower mid level ones such as an Ebonghists should be a brutal fight for any three of us.
As for power. What? Are inquisitors not going to use considerable force when facing the enemies of man? In the books you mention far greater forces are brought to bear. If you are concerned about PvP then a decent running start should keep you out of grippy range. My role in combat is clear. Provide local support and form a solid backbone to the force that others can maneuver around to take the fight to the foe.
As for my role in the group, considering that i have not even made my fist IC post i feel you have been a bit preemptive. If Zhevon feels he cannot use Malek's skills i'm sure he will make this known. Should Malek appear. No Malek won't be slipping by sentries however a well controlled skull could. furthermore my contacts in the Ad-Mech themselves could be invaluable, properly manipulated.
As for any point on the other characters i have considered some of these points myself but would also consider some of them excessive. after all as a staunch fan of 40k for many years i have to say those taking it too seriously are missing the point. this is a universe in which you can march 10,000,000 men to their deaths in a single day and get clapped on the back for a good effort. though i do try to restrain some of the Grim Derp myself.