The problem is that there's no reaction to there being a sudden surge in busy times...
Most parks will, on quieter weekdays, run one train... This is no issue of course, why would you run more than required? However many of these parks will, in the event of queues developing beyond a time frame (I'd say maybe 30 minutes? Maybe 20 depending on how nice I'm feeling) add on an extra train to cope with it...
Why Thorpe can't do this (Chessie did in my time on Fury and Rattlesnack, Vampire was a different thing though due to how the transfer track worked) I'm not sure though, perhaps they're still struggling with their maintenance teams?
If Rush and Rumba were open it would make a difference to the queues... Likely not a lot, but every little helps...