Well, yes and no.
Yes access to the south platform does interfere with the southernmost main track, but in practice there's not much reason for CN to ever use that track anyway, since it doesn't lead to the York Subdivision, and there are two other tracks to the north which do.
But the track configuration certainly does cause unnecessary conflict between eastbound and westbound GO trains, since there's only one track to the south of the main CN pair. It's quite a frustrating situation considering how Bramalea is a key turnback point for counter-peak service.
Here's a diagram I made a couple years ago showing the existing layout and its primary track users (not necessarily the track owners), as well as the modest change it would take to resolve the conflicts for counter-peak trains.
Here's the 2018 track layout in real life, with tracks highlighted:
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