Not sure why but I'm struggling with 15+ missions. I'm at 15, have an 800+ DPS assault rifle and defenders. But when ever I do a defend mission it seems I'm just being chewed through. I only drop down tier 1 walls, usually metal. I can upgrade to tier 3 but sometimes that's a chore, like if I'm doing metal walls in a forest. Are tier 3 wood walls better than tier 1 metal? Most of my traps are level 5+ but most are green. My hero is a 2 star level 15 blue soldier (Banshee). Not sure what I'm missing.
Any ideas on how to improve?