system
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human
[WH40k] Are the chaos forces vastly superior to the humanity ones?

In the times of the Horus Heresy, half of the Legions turned to the chaos. It seems that for every space marines' different kind of unit, there also exists a corrupted version of it, which is supposed to be a better one as it has been enhanced by the ruinous powers. Also the traitors have demons, chaotic instruments, weapons and powers, and even some of their primarchs, things that the loyalist don't have. Do the loyalists count with any weapon or unit that the traitor ones don't? Or... are they at least bigger in marines number?

And a second question. Does the traitor marines are stronger in combat than the loyalist ones? They are supposed to have been empowered.

Reading all this things I have written, it seems humanity have not even an opportunity to survive, isn't it?
gpt
Outright more powerful?  Very often, yes.  Less reliable?  Definitely.  Can't trust daemons to do what you enslave them to do, after all.  
Their lack of discipline is 9/10 what gets them killed by loyalist forces.  You can be a crazed Khornate Berzerker Marine who's 12' 7" outside of armor and absolutely bulging at the seams with muscle, but that won't help any when a melta blast disintegrates 80% of your body.  
The CSM numbers overall are probably much higher, what with Daemonculaba dickery+ Chaos dickery+ Chaos God dickery+ Dark Mechanicus dickery+ outright stealing loyalist geneseed.

Its just like the Night of the Wolf.  Angron pretty solidly beat Leman Russ 1v1, but since the World Eaters didnt fight with/for him, he would have been killed by Space Wolf Marine packs.  

Also its mentioned by that one Ultramarine who was undergoing censure for making practicals on how to fight other Space Marines.  The Word Bearers can be at one moment tactical geniuses and curbstomp the shit out of people, while the next moment they worry too much about sacrifices and pleasing the Warp Gods and get their shit pushed in 6 ways from Sunday.