NPCs aren't too bad to wade into for the bomb, though of course it's not smart to go for if you have aggro on them all. Borg are often even easier than some other NPC groups to bomb due to the various drones that either try to walk into melee to attack or just have weak fire (i.e. aren't heavy tacticals).
It sure kills packs of drones pretty well, though, and certainly makes KAGE a breeze.
Turrets are fragile, just don't put them anywhere in front of 15 mobs. It's like complaining about dogs who ate your piece of meat even if you threw it away in front of them. YOU are supposed to take the aggro, not your stuff.
The medical generator is fragile too, and it's supposed do be destroyed if you're surrounded by a lot of mobs too.
Quantum mortars are the best thing ever. You set them up way out of the way, so they don't get attacked, and they do almost 1000 damage to multiple enemies when you've spent some skill points. Against slow enemies like the Borg or trapped enemies (science officers + electro-gravitic field), they're just devastating.
The cover shield + generator trick works very well. Also feel free to plop a force field dome over it for even more resistance.
An engineer is just a walking fort when deployed correctly. It's not meant for direct damage (that's what team's personal weapons are for) but its a support function.
Engineering fabrication kits would create Battlemechs instead if they were meant for an assault function.
Quantum mortars are another very useful thing because if you can stall an enemy with science skills (EG field etc) the next second they'll be under severe threat of death from above.
The evil thing to do is attract aggro, lay mines in a choke point and use a cover shield to block it off. The combination of mines and quantum mortar can take out just anything - especially where chronitron mines have a very nasty slow effect to keep them within mortar blast radius.
STF Flight Instructor since Early 2012. Newbies are the reason why STO lives and breathes today. Do not discriminate.