Yup, I got caught up in that also. Trains were indeed leaving half-empty. I complained to the bloke on the platform and he directed me to his big boss on the bridge. I asked him why they were letting half-empty trains leave the station and he said the trains had to run on time. Which is fair...
Happy with the service for Saturday games but for midweek games could do with a major cab rank and/or a dedicated bus service serving Brighton/Hove/Shoreham town centres rather than just P&R. Current setup has a significant effect on midweek attendances IMHO.