There is a distinct issue with potential (indeed, on a ride scale, they could do so much more than have numerous 200 pph attractions) at the park, but the earlier closures are based around the locals...
Vampire is the main problem, as it's located right on the Monkey Puzzle and Hotel (opposite side of the lift hill), this means late openings (I think 10 was the agreed latest ever time they could open) are not a viable option...
Not opening till 8 is silly though, especially when you have the best transport links in the country...
There are lots of things the park could do to improve itself (better overall throughput attractions, pushing throughputs on their big rides, fixing itself up on a massive scale, actual new attractions, etc), just a lack of budget given to it... It's a weird one indeed...