If a park like Alton can't do 8 hour days then there's a problem. You reap what you sow, people expect to not eat there and go in with a plan of attack to get the most out of a 4pm close. The ends start justifying the means because the hours and operations drive the behaviour.
The park always has decent attendance during Scarefest when at least some entertainment is laid on and the opening hours are reasonable. If the park started to operate 10 - 18 or 11-19 of peak, visitors would change their behaviours. Even if it took time to bed in.
There's no evidence to suggest otherwise. Those who defend 4pm closes with ”but the park is quiet and I got on Nemesis 4 times" should look at the bigger picture. Anytime I take a friend or family member who hasn't been in a while, 4pm close is always the first thing they bring up as a concern. "Are you sure we can get everything done? Is it really worth it for just 6 hours?". How many other people are put off going because of this?