I mean, the Crossfield class was constructed specifically for researching spore drive as a potential warp alternative, so we have to assume the spinny saucer is a required part of that technology and the structural weakness is a necessary trade-off.
Obviously the off-screen reason is that it looks cool.
I do wonder why Discovery and Glenn are NCC registries though rather than NX - given they are the only ships of their class, and experimental in more ways than one.
It looks cool when the spore drive activates, but the gap in the saucer section just seems like a structural and logistical weakness.
I mean, the Crossfield class was constructed specifically for researching spore drive as a potential warp alternative, so we have to assume the spinny saucer is a required part of that technology and the structural weakness is a necessary trade-off.
Obviously the off-screen reason is that it looks cool.
I do wonder why Discovery and Glenn are NCC registries though rather than NX - given they are the only ships of their class, and experimental in more ways than one.