I think Boxhill gets a far better service than it deserves. I don't think Horsham–Dorking deserves more trains, but they should be faster to London to entice customers back to the railway. The ideal situation would be separating the Epsom stoppers out again, and giving the Horsham trains fewer stops (as opposed to the Dorking ones). SWR should be able to cater for stations like Boxhill if they bring back more services to Dorking. During engineering works a few months ago, I noted that Victoria-Epsom-Horsham took about 45 minutes. I think something that did Victoria-Clapham-(Balham?)-Sutton-Cheam-Epsom-then all stops except Boxhill would work well. Obviously, I know nothing about whether this fits within the timetable.
A lot of time could be saved on the Up trains too. Up to 7 mins at Dorking, a few mins of dwell at stations en route, then as many as 8 mins outside Victoria. The 08:xx off Horsham is booked into Victoria at 09:49 but routinely arrives at 09:41. Lots of angry muttering from the commuters! My Down journey is currently 8 mins faster than the Up.
Ranting over, hope this helps give perspective. More / faster trains please, GTR!
I do agree that Mole valley line services do need speeding up, they are horrifically slow, especially the Southern ones, with too much pathing time.
Regarding Box Hill i do think it is overserved on weekdays with every single train stoppping there, but on weekends with the considerable leisure draw to the area i do think it is right that every train on the weekends stops there, i know up until a few years ago the vast majority of SWR serviced skipped Box Hill but id say it is an improvement that SWR stop at Box Hill.
That 08xx off Horsham 2I13 yes does have a longer than usual dwell at Clapham and extra pathing time into Victoria, getting in at 0949 whereas most other ex Horsham Mole valley services get in at xx45 so its only 4 mins longer in that respect.
As for retiming it into Victoria earlier, it might be possible but not without some tweaks to platforming, which then might throw up other constraints. 2I13 ex Horsham is booked into pl10 at 0949 (based off the June24 timetable) and has to wait outside Victoria for the 0946 2B94 to Selhurst to depart pl10. 2I13 forms 2B36 to Epsom Downs at 1000 so to get 2I13 in any earlier you'd need to have an availible platform 0942-1002 of which there is only one in the june timetable on the Sussex side. Pl17 is free 0942 to 1002 however with fast line services 1W13 ex BTN due in at 0941 into pl13, 1B15 ex BOG due into pl16 0945, and 1R95 ex REI due into pl19 at 0949 and a 0946 littlehampton departure from pl15 you would not be able to find a path for 2I13 into pl17.
All other platforms are occupied within the relevant time frame on the Sussex side, however (again based onto the june24 timetable) you could POSSIBLY route 2I13 into pl8 (shared between SN & SE). However in order to route 2I13 into platform 8 you would need to move the Southeastern units (2U66 which forms 5L66) occupying the platform 0954-1020 to pl5 which is free 0940-1021. You would then need to retime the ECS 5L66 a few minutes earlier from 1020 to 1017 to free up pl5 for 1P20 ex RAM.
So in a long winded explanation yes you could probably get 2I13 08xx exHorsham into Victoria a few minutes earlier but it would require the cooperation of Southeastern to adjust their platforming and timings slightly. Whether GTR considers this worth the effort im not sure.
I suspect the occaisons in which youve arrived earlier have been as a result of 0946 to Selhurst either being cancelled or replatformed and thus freeing up a platform for your earlier arrival.