No it's not bad. You can go Thameslink through to Bedford and then change and there are only 4 stops to Sheffield. Change again and a local train then to Barnsley.
Station Arr Dep Travel by Operator
BRIGHTON STATION 08:49 Train SOUTH CENTRAL
LONDON VICTORIA 09:40 09:40 Tube
LONDON ST PANCRAS 10:25 10:25 Train MIDLAND MAIN LINE
SHEFFIELD 12:42 12:50 Train ARRIVA TRAINS NORTHERN
BARNSLEY 13:16
DURATION: 4:27
BRIGHTON STATION 09:49 Train SOUTH CENTRAL
LONDON VICTORIA 10:40 10:40 Tube
LONDON ST PANCRAS 11:25 11:25 Train MIDLAND MAIN LINE
SHEFFIELD 13:42 13:50 Train ARRIVA TRAINS NORTHERN
BARNSLEY 14:16
DURATION: 4:27
Going back
BARNSLEY 18:14 Train ARRIVA TRAINS NORTHERN
MEADOWHALL 18:34 18:39 Train MIDLAND MAIN LINE
LONDON ST PANCRAS 21:49 21:49 Tube
LONDON VICTORIA 22:36 22:36 Train SOUTH CENTRAL
BRIGHTON STATION 23:28
DURATION: 5:14
BARNSLEY 18:52 Train ARRIVA TRAINS NORTHERN
SHEFFIELD 19:23 19:39 Train CENTRAL TRAINS
NOTTINGHAM 20:25 20:35 Train MIDLAND MAIN LINE
LONDON ST PANCRAS 22:44 22:44 Tube
LONDON VICTORIA 23:32 23:32 Train SOUTH CENTRAL
BRIGHTON STATION 00:51