If the "No Escape" rule was more consistent and conscripts weren't able to readily receive an order to fall back and shoot, then wyches would be a great counter. But as it stands, it's not the best option... by itself.
When playing conscripts, you just have to play the mission, and try to avoid them. When they DO get on objectives, send in a boat of wyches and force them to fall back. Use your boat too, to force them to fall back off the the objective. You'll take some losses, but remember, just play the mission and focus on getting VPs, not killing the blobs.