Chaos and multiplayer

I'm overwhelmed by the amount of stuff Chaos can bring to the table. Bretonnia has good cav and ranged but bad infantry, Vampire Counts has good infantry and monsters, no ranged. Chaos afaik has everything and it shifts too much. It used to be ( before CoC) that demonic factions had only demons, which for me meant bringing ItP and magic damage. Then came CoC and WoC got demons and Demons factions got from marauders to Chosen with mortal lords to follow, so do i bring magic damage, do i bring ap or are they gonna spam marauders?. I then spent 5-6 months perfecting Norsca to counter WoC. Then came Tides of Torment and now WoC... can play like Norsca, bearmen dreadmaw and chimera. Oh and also Slaneesh got a infantry ranged unit but i guess that's alright, khorne doesn't have that but has artillery, they don't have artillery.

Am i supposed to look for faction weaknesses when making an army or not? If the idea is to make an army that can deal with anything I'm playing wrong. Are demons and Norscan capped for WoC? Are mortals capped for Demonic factions? Should they be or is this completely balanced? After all I'm new to rts multiplayer, apart from getting nuked in supreme commander.