We actually have no idea how much the Empire was able to get from the
Defiant. Hell, we don't even know if Hoshi's attempted coup was successful (for all we know, Imperial forces shot her out of the sky).
And I happen to agree with
@HellRod, I find the TOS aesthetic extremely dated. I much prefer the Discoprise. I'm totally on board with it always having looked like that.
Although I admit I'm curious as to what will happen to the ship when the crew complement inevitably doubles to 430. Maybe that's what gives us the TOS look.