- Voyager is an older Ambassador class ship. This means there's a larger crew, so more people to kill off without severely hampering the ship, and it can stand up in a fight longer against Kazon raiders and Vidiian Cruisers, even though it's weapons and shields and stuff are outdated compared to Starfleet's present ships. So it's an older vessel with older tech more prone to need repairs and stuff but still able to survive.
I like the general idea The whole spin on it being an out-dated Ambassador class ship is pretty cool, but what if it was a Galaxy class that had the saucer section destroyed in its first encounter. The drive section is not vary large and the crew has to interact a lot closer, tempers flare and more problems arise. also without the saucer section's phaser array I believe it would be somewhat under powered, although it would be faster and more maneuverable, I think a lot of the species you are talking about would be more than a match for it. I don't know, what do you think?