The scheduled travel times for GO local trains were all shortened by a few minutes in 2020 due to the drastically lower ridership, which produced shorter dwells at stations, as well as faster acceleration due to shorter trains. It sounds like (contrary to GO's proclamations of low ridership), ridership is returning to levels which require the extra schedule padding which was present pre-pandemic.
Or, instead of slowing down train schedules, they could keep the local trains short (e.g. 6-car MP40 or 8-car MP54) and add supplemental express service during periods where more capacity is required. On LSW, they obviously need to reintroduce peak-period express service from Niagara and Hamilton (these can be longer trains), and during the midday they could run an hourly express service from West Harbour (cutting the local service back to Aldershot or Burlington).