As said in other threads bad pathing into Woking is the main cause for the current slowness, I believe.
I'm just coming in to this discussion off the cuff as it were, so am unaware of previous comments relating to the Alton's, and as such I do not make any criticism of other's views. I may also be going a bit OT for this thread (sorry), but for the sake of the issue of 'pathing in to Woking (Alton's), I will just add the following.
If talking of pre pandemic times, yes the Alton's did hang around between West Byfleet and Woking, primarily to allow the Down Pompey Fasts to overtake and swing over to p5 (DSL) at Woking, where they departed at xx25/55, the Alton's then following them. The reason I believe the Pompey's were timed down through p5 was simply to ensure that on the half hour that the non stop (at Woking) fast Weymouth's ran, they were given a clear road (as in clear aspects) down through p4, although I may be getting my timetable details mixed up here - sure there are those of you who have the relevant TT's to hand (I do not).
Also seem to remember that if some 'spare' time in the Down Alton's wasn't used up in the Woking area, they would have had to sit for ages at Brookwood due to timetabling conflicts and connectional issues that would cause problems in the Ash Vale to Aldershot area.
Aldershot was always an area of TT conflict, given the nature of taking all services in to account, not only including connections at Ascot/Guildford, and out of/in to Alton line trains (at Aldershot), but critically crossing margins at Aldershot North Junction, and to a lesser extent at Aldershot South Junction (with North Downs services which SW planners could not tinker with in TT terms).
In my past experience of timetabling conflict areas on the SW, Waterloo/throat is the lynch pin in any timetable (overall), but second to that is Woking Junction, and (for the outer sub area) I would wager Aldershot came next in complexity with Guildford in 4th position. To clarify in the pre/a.m. peak period (0530-0730) with numerous empty stock movements leaving Farnham depot, Aldershot to Ash Vale/Aldershot South Junction was a serious headache if one wanted to find additional pathway slots, be it for post weekend engineering associated moves or as was the case with the stock cascades that were required during the capacity increases that saw the 458's increased from four to five cars.
As said, getting too far OT now perhaps.