I would like to say before this, that I love the TOS designs, I would watch Discovery if it looked identical to TOS, but a lot more people wouldn't. and the show wouldn't sell. People would look at it and laugh.
So the Discovery is a ship that is more than twice the length of the original Connie, with a saucer rim that is supposedly half of the Connie, and a crew that is half the Connie. I'd love to hear your justification for all this?
Different mission profiles requiring different personnel. Being in the middle of the war may also be stretching personnel thin.
Remember the Discovery is primarily a science ship, not a warship, in fact whenever they're in combat they seem to get pretty beaten up because the crew is mostly made up of scientists, Lorca and other crew comment on this a couple times.
They're probably meant to operate closer to home, not out on the fringes like the Enterprise.
Also in the 2250s the Enterprise also only had around 205 crew members, they didn't have 300-400 until the 2260s.
Here is a fan made comparison of the two ships using the size that was just revealed, the inner saucer is nearly the same size as the Connie's
Bigger doesn't always mean better, the Discovery has a bigger profile, making it harder to miss, the Enterprise is smaller, probably more manoeuvrable.
