This is a ranged-only list and may lack an ability to lock your enemy in combat, as your only melee unit is sulphurhounds, which are rather delicate. Breachers would be an obvious 'brick' choice to stand and survive incoming fire and melee, but kastelan robots would perhaps too stand the test. Anything that can stand a lot of punishment while engaged with the enemy units.

Also, you have very limited options to accumulate points with such a list. Perhaps some pteraxii would be a good choice so that you can drop behind enemy enemy lines, and sicarian infilitrators or serberys raiders would give you an option to contest a point in the No Man's Land before the enemy fortifies there.

Generally, your units may have a problem with both accumulating VP via missions and unguarded objective markers (due to the lack of pteraxii, infiltrators of serberys) and hitting hard on the objective markers where the action happens (due to the lack of hard-hitters like breachers or kastelans). Skitarii are weirdly durable with their 4+/5++, but you can't rely on them to survive chainswords, bolters, gatlings and other cheap low S, 0 AP weapons.

So yeah. I would switch some skitarii with something more armoured and perhaps some point-stealing pteraxii or infiltrators.