Well, impulse agility is something the Jem'Hadar smaller ships excelled in. It makes sense that Starfleet's most antiquated assets would need some beefing up in that department...
Having a rolling door cover a semicircular doorway is physically rather challenging, so that's probably not how Starfleet would close the hole if they wanted to. But the Excelsior
was introduced in the same movie that introduced the enclosed Spacedock Earth, supporting the notion that Starfleet sees merit in enclosing vacuum inside walls. With the space station, it's for the purpose of having ships inside, somehow. I'm all for it being for the same purpose with the ship! The Lakota
greeblie could well be a utility spacecraft that has two bulky and angular cargo sections - possibly a landing barge for assault purposes, perhaps a deep space self-repair auxiliary.