They may be cheap but with no armor, low I, and LD7 they fall apart like mad. They just can't dish out wounds and take too many in return. Assault weapons or even the old genetic buffs they used to get would be great. But right now they get put on the field for the sole purpose of getting killed.
But I think that's the point. Think of them like slightly tougher guardsmen with a bolter and two CC weapons, and you'll find their point-worth to be right on the mark.
They are very good at what they do... now if you want them to be a dedicated, winning close combat unit, then they have a long way to go and would easily cost two, three times as much.
So they are a good unit. When compared to other things that fill no role, or have another unit that does it so much better (stealthsuits, sniper drones, gun drone squadron, skyray), the kroot really do shine as a good investment that remains relevant to 5th, which is saying something for this codex.
Oh, and Ravenwing squadrons need a rework to not bleed kill-points, and deathwing need a cost reduction.