In the Up direction its often much quicker to take the Southampton to Brighton Service and change at Brighton because of the high frequency on the Brighton Mainline.That is the same negative? A 25 minute connection at Barnham or Chichester isn't a great prospect for anyone travelling from East Surrey or North West Sussex beyond Cosham. However, those are the difficult things which the timetable people have to balance and you can understand why Brighton to Portsmouth connections were favoured over the Southampton ones.
(In practice, most people will, I expect, reduce the wait time by catching the stopping portion on the Arun Valley.)
If you want Redhill its quicker to travel via Guildford and the North Downs Line. From Cosham and beyond it will now be more convient to change to the 2TPH Victoria service from Fratton.