If your goal is not to have realtime performant rendering and you dont care if you spent a few minutes per frame then I don’t see the reason why you will need to use a game engine for the task when offline renderers already have gotten fast enough to render a decent HD Frame for archviz from a few miinutes to 10+. Both GPU and CPU are going real fast these days. with incredible in built denoisers helping things out if needed.
You also have to keep in mind the setup time, the setup time to import arrange and make scenes “compatible” to work with a game engine even if you are not creating a game or looking for performant scenes and then spend further time on managing proper materials and lights (which are still limited compared to offline renderes) all this is time consumed per project.
I would rather work limitlessly in a 3d application and send a frame to an offline renderer and wait a few minutes longer than spend extra time and worry about crashes and setup times in UE.
A recent project of ours almost suffered the same fate when we attempted to render in UE, in the end we found it too risky and time consuming, the project took a day longer for rendering but worked as expected and in a well predicable fashion + we got extra passes for compositing for free, something still extremely limited in game engines.
In short if you don’t want want the scene to run in realtime or near realtime as in (5 -10 seconds per frame rendering) then no reason to go in engine.