I wouldn't necessarily say the trueborn units are terrible, but at 1000pts and with only wyches in your troops section, the trueborn are priority number 1 and aren't going to survive very long.
Wyches are pretty much universally acknowledged as a bad option in our codex, and the only lists i've seen including them are designed specifically around getting them into combat. Even then those lists are still only played for friendly games.
The Archon I'm assuming you were planning on putting with one of the wych units and aiming for combat? If so you'll really want to give him some kind of weapon upgrade other than making him slap ineffectively at the enemy. If you really want a combat warlord then the Succubus is a much better choice.
The Scourges are a good choice, you may want to think about whether you want haywire blasters for anti tank reliability or heat lances for shorter ranged versatility and punch, or blasters for mid range jack of all trades. Two squads in a game this size wouldn't be overkill, and they have the added bonus of still getting a save against most standard guns like the bolter, which neither wyches nor warriors do.
Most of all though: What style of play do you want, do you want to attack up close and personal in combat, or would you rather stand off and shoot. Coven units are much better for the former (Grotesques and Pain Engines particularly, not so much the wracks) whilst warriors and support units are better at the latter. If it's the former you want, I'd strongly suggest getting your hands on a copy of the coven supplement, just be aware that their anti tank capability is limited.
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