I'm not sure if making a doomsday ark a barrage would make it much better. With your range and AV13, it's not that squishy. Especially with a lot of recent missile spam meta. What it really needs is an Ordnance profile.
I think stacking lightning field requires an FAQ. It is a little grey and simply stating it doesn't stack would also imply you can't stack other abilities like crucible since they're worded similarly. Abilities that are specifically measured from the cryptek and not the unit like nightmare shroud would still stack being seperate sources. But I do question abilities where the unit as a whole is the source. A good example for arguing LF not stacking would be the Eldar codex and its new FAQ. Runes of warding add an extra D6 to enemy psychic tests. Taking two of these shouldn't stack because it's a passive ability. It doesn't say add an extra D6 for each runes of warding in play. The enemy simply adds a single D6 because the runes of warding is active. LF sort of falls in the same situation. The unit as a whole has lightning field and when charged they deal D6 hits. It would need to say D6 hits for each lightning field in the unit. You can also argue the polar opposite since LF also states if a unit assaults a crypek OR his unit... You could apply that the cryptek is the source and not the unit which allows you to have two individual sources of LF. Assaulting the unit that has a cryptek also means you're assaulting the cryptek. I think for now, I'm staying away from stacking some of these abilities to save some headaches.
Though I don't think it played a big role in my last game, I am frustrated that Nemesors adaptive tactics doesn't work in reserves/Dawn of war even though it's worded exactly the same as logan grimnar's similar ability and his does. To my knowledge, every codex can't use start of turn abilties or powers when entering from reserves except for space wolves. But then again this wonderful logic is the same as some of the last psychic power faqs spread throughout the codecies. Yay for dart boards!