Ive been thinking, from a purely dramatic point of view, you could say that artificial black holes dont possess the power to spahghettify things, only compress and eject them (sort of like an external warp drive through time and space).
Forgive me for my shoddy science, but dont real lightning bolts possess thousands of times the power than that of which we are able to create artificially? I mean, for the purposes of testing housing and metal devices, artificial lightning is a good substitute, but it isnt the real thing. The same effect could go on with Black holes.
As for his ship, yes, it did get torn in two, and then blasted to many more pieces by the Enterprise - BUT, Canon be damned, the countdown comic's backstory that the Narada is infused with Borg tech MAKES SENSE. The ships interior looks like a Borg Cube, so It isnt a stretch to assume thats where the technology is from.
If it is filled with nanoprobes, it has the power to repair itself. So Nero might not have a single 5 mile long mothership, but after a while he might end up with 2 large ships and a few smaller ones which have "grown" propulsion systems.