If they made Destroyers Bolt Pistols Assault 2, each, it might make them more worthwhile. 4 Shots at 12" each and can still charge means each marine has the firepower of 2 Rapid Fire Tac Marines.
Sure, its a bucket of dice with 10 Destroyers (40 shots) but its close range and you sacrifice an Elites slot for it (32 shots if you take 2 Rad Missile Launchers) while it also remaining Bolt Weapons.
Make the Phosphex Bombs on the Sarge 5pts each instead of the double it is now or keep the same cost and boost the range a bit.
For Specials either have the Marines be able to swap both pistols (2 Plasma/Flamer/Inferno; 4 total in 10 man squads) and/or make the radmissile launcher Heavy 2 (Assault 2 with Suspensor Web).
Some cost adjustments here and there and they might be more worth it like this.
I have 20 Destroyers and it kills me that I have no reason to ever use them outside of games we're playing for giggles or special scenarios.