GO Trains do not need to and generally are not frequently mixing with freights in the USRC, and eventually that will be the case across most of the network. The post you quoted also quite literally refers to having better single level trains. There is no reason that we need to have 4-5 minute dwells at Union, and assuming we can even regularly beat that you are already well over 10tph. There are plenty of systems with mixed rolling stock that do high frequency - even with locos - and GO is pretty darn close to an entirely uniform fleet already, at least performance wise! Better performance does not require blowing things up, it means dumping old ops practices that are impractical on a modern high frequency railway like last minute platform announcements.
I am indeed aware that Toronto is in North America, I am also aware that curvy is relative, speeds can still go up especially for the south tracks! We should be aiming to be much more like Europe and thats why we are doing things like adopting ETCS among many other things behind the scenes.