Approach control is approach control can't really help with that one. Strange decisions by signallers at the end of the day they are just judgement calls that some you get right some you get wrong, some are made with good intentions. A late running services (that is failing PPM) regardless of stopping pattern has to be added to the conveyor belt that is the BML at some point and can't be held indefinitely and will end up in front of a faster service. After all the next gap for the slower service will be taken up by the same service but half later. Quite a lot of the decisions that drivers don't like come their own TOC control via NR control and their train is to be that hours sacrificial lamb. The BML is a very crowded railway and I can't see that changing anytime soon, but performance does improve when the thinned out service operates on the conductor/guard strike days.
Most of the suburban side was designed for 8 coach trains that could pull right up to the signal and didn't have to stand a coach length from the signal when at red at a junction. I've lost count of the amount of times that a 10 car 2R or 2J is hanging over Selhurst junction waiting for Glocester road junction, which in turn is preventing an up 2L, 2P, 2M, etc etc from crossing over Selhusrt Junction and now themselves over hanging Cottage Junction thus preventing the next train trying to join the up London Bridge Bridge slow line. Even worse all the junctions are controlled by three different signallers with their own ideas on how to regaulate and which train they want to have priority if they I not on time. This is happens almost everytime a train requires the down Selhusrt spur in the morning peak. Now LOROL have a tighter PPM than all service groups on GTR they nearly get first service over everything else, in fact there are now controllers employed just to ensue it happens.
So in fact your service from East Grinstead, Uckfield, Caterham, Tattenham Corner, Redhill, Reigate, Tonbridge, Three Bridges and Horsahm in fact any service on the up slow lines for Norwood Junction, London Bridge/Thameslink Core that is delayed at Windmil Bridge Jcn could be because a 5 coach train to the East London Line has priority at a junction on another line that you can't even see from either your driving cab or coach window.
Whether we drive trains, signal trains or work in control, getting the commuters to and from London on a daily bases on time is becoming a ever increasing complex puzzle to solve and it's got to be done safely. There are strange regulating rules we have to follow just because it's in the TOCs contract and all the TOCs plus NR agree a common policy even if most if the staff on the ground don't get the hear about it, but we as signallers get to hear about one way or another as it what we have to follow when we regaulate.