I don't like the idea that VOY couldn't have been anything if the writers were up to the challenge.
The Hirogen, Q, the Vadwaar, the Caretakers, the Borg...I think they had opportunity to create larger arcs but generally shied away from them.
Epic means larger than life and by that definition, half of Star Trek's single episodes are epic. "The Chase" wasn't epic or "Year of Hell?" The lives of half the galaxy weren't hanging in the balance of most episodes of the other series either.
Epic I think is a quality. I and I think even ship board episodes could have been epic if the writing took the characters to sufficiently epic heights. Heck, what happened to Kes alone when she left the ship was pretty epic. If they allowed characters to actually change, I think the impact of that change on the viewer too could have been epic. But always, the reset button was set on characters just as it was set on the ship being as pristine in the last episode as it was in the first.
That the baddies they did come up with weren't interesting, or written that way, doesn't have to do with the ability of the format. Heck, Moya too was on a long journey looking for its crew's homeworlds.
Moby Dick was epic - what if a continuing storyline was of another ship chasing Voyager through time and space for a perceived or actual wrong? Bialar Crais/
Maldis/Scorpious meets Arturis/Captain Ransom/other... Not just a single individual though, more like a crew, an anti-Voyager maybe, or the Voth, or something. Continuing storyline, different type off attack and ramifications every episode...
A baddie that showed up every so often in a new and interesting way. The Borg basically did this, catching up with Voyager every how often even though Voyager was out of core Borg territory. If all you're looking for is trillions of lives at stake, what if the Caretaker's people showing up to cleanse half the galaxy to cover up their shame? Or, wait, the Continuum started to tear apart the fabric of the universe during their civil war.