I was thinking that warriors had value for two reasons:
I am not sure exactly how to value these and it'll take a while for me to figure out an objective measure, but with DE troops being cheap, potentially having a low model count (we can just stuff them on a raider with other better things), and not being entirely useless: the cost of going from a patrol detachment to a battallion detachment is pretty minimal.
I don't think Warriors make much sense as a heavy weapons platform. The 70 point tax of getting 10 warriors is just not worth it. We can get a venom, trueborn, and scourges all for less/equal points but with better heavy weapon options.
BUT, I think they offer a reasonable value for special weapons and syabrite wargear. The value isn't quite as good as trueborn, since you can get 4 special weapons with 5 models rather than just 1, but to maximize trueborn value you need small squads with high special weapon counts and that is scary with such a weak unit.
I really like the idea of sticking a warrior squad with a blaster in a raider with a melee squad. It gives the raider some value after it has dropped off the melee squad, counts towards command points, and is not very expensive. Adding the agoniser and pgl are points dependent, but can add some more versatality to the squad.
It is true that a 5 man trueborn squad could bring more firepower, either with blasters or heavy weapons, but I think that puts too many points into a single raider. Raiders are tougher, but they still aren't that tough, so I want my points spread evenly and not bunched up in one relatively vulnerable target.
However, the more I think about it, the more it seems like sticking a warrior squad in a venom is a waste. A small warrior squad isn't good enough to warrant its own transport. Why not put scourges, trueborn, or assault units in the venom?