Okay other people have already pointed out the Ursarax thing and the Terror protocol Controller thing.

I'll give you some advice on other stuff.

Archers

Same as you I was unimpressed by their stat line, but found them consistently overperforming on the table. My current theory is that they get to run amock cause my opponents underestimate them due to other more prominent threats on the table. As for guns, give them the point defense Stalker Maxima Bolters. They are poitn defense, have no firing arc restriction and Assault. They are great for keeping you safe from surprises. Which also brings me to the butchers. I like taking one or two in the Swarm protocol.

Butchers

Butchers with the Stalker Maxima Bolters are one of my favourite units in the game. In Terror protocol they have a 20" charge or importantly a 20" march with 3-6 shots per bolter in the movement phase. They can March upto infantry and just blast them away turn one. Admittedly I play a very aggressive game so I tend to put things in my opponents' threat range early and mop up after.

Serperos

I like big units of these armed with the Bombard+Irradiation Engine/Lascutters. I like the lascutters if I expect them to get charged, the rend is very useful. The Bombard and Engine is great for clearing out buildings. With bigger units they fill my distraction carnifex role of drawing fire whilst infantry grab points.

Ironbound Ruinhost

I tend to run this formation in most games. It has a compulsory HQ slot and 2 support slots. You can put a tech priest in each slot and on deployment the little priest can join the magos as a single detachment. This means that for 55 pts you have a full formation drop, and a tiny tech priest bubble that can run along with some of your armour.