@Phthisis
It must be admitted that the Dictator was purpose built to close. Prow armour, torpedoes and lack of range makes it a line support ship. This has its ups and downs.
The Dev, on the other hand, is more versatile. With the extra range and speed it can provide support from a safer distance, and at 190 pts it provides a better AC to cost ratio than the Dictator. When the enemy closes to 30cm it puts out as much firepower as a Lunar broadside (or both broadsides of the Dictator), while still maintaining a resilient aspect and providing AC to the fleet. For just 10 pts more than a Lunar, that's pretty good.
But the versatility comes in being able to use it as an attack carrier. When breaking the line it has 75% of the Lunar's direct fire capability plus 4 AC (minus torps). It also has better speed to get into position and an extra turret. All this for 10 pts more. Not too bad. What it really loses out on is the 6+ armour of course. The solution here would be to either approach obliquely (mitigating both the prow vulnerability and the speed bonus) or to provide a preponderance of targets with the soft prow. A fleet consisting of Slaughters, Hades, Devs and Executors, for example.
You could make the argument that neither of these options is as good as the 6+ prow and that despite the 50% greater direct firepower when used as a line breaker, this isn't as good as the torpedoes of the Dictator. You'd be right. The Dictator is a better carrier of the line. It costs more though, and is not as good a support carrier. It's slower, lacks range, pays for armour that wouldn't be used and has less firepower.
So when you compare the Dictator to the Dev and argue that the Dictator is superior you're right, when looking solely at the role of carrier of the line. I don't think that the Dictator is tremendously superior in this role, but it is easier to use. The Dev requires a little finesse or a themed fleet, and lacks the punch torps can provide. But, meh, it's cheaper.
You might have got such opposition because it seemed like you were making a flat statement that the Dictator is greater than the Dev full stop. If that was your intention, then we'd have an argument. For the role of carrier of the line, I'm willing to stipulate that the Dictator is superior and more purpose built.
The question I think is does Chaos need a carrier of the line equal to or better than the Dictator? My initial thought is no. Firstly Chaos isn't really an attacking line fleet. They're more like circling wolves. OK, yes, you can construct a closing Chaos fleet. Sure. But if that's what you want to do then the Dev is a fine ship. If we start trying to give Chaos a carrier of the line like a Dictator then why not other ships of the line? Why not a Lunar analogue? Or a Ret analogue?