I stuck in another outing I was thinking of: Poole (for Brownsea Island), which is about half as far away as Battle. As it's much closer it only takes 1 hour 20 including a 10 minute change at Southampton Central. However a day return for this costs £20.10.
It gets even more absurd if I look at a trip to, say, London. There's a handful of possible routes: I can take a Southern train via Horsham which takes a smidgen over 2 hours, or a South West train via Winchester or Guildford which is around 20 minutes faster. The one using just Southern trains costs £22.10. The South West trains route costs £38.30.