When I lived in Waterloo I avoided the 25 local at all costs, and most other people seemed to as well. The express services, on the other hand, were great. On Fridays all the express services would be packed (every 15 minutes to Square One, and every 30 minutes to Bramalea/York) while the hourly local buses were fairly empty.
It is excruciating how slow the local branch is. I literally had a nightmare one time where I dreamed that I had mistakenly gotten on a local bus at square one and started panicking about how I was going to be trapped for two hours before the bus would get to Waterloo. Thankfully I woke up and found that I was in my bed, not the route 25 local bus.
If GO thinks that students are captive clients who will take the bus no matter how slow it is, they are sorely mistaken. From my experience, if there weren't any GO express buses running, students would seek other options like Greyhound or carpooling, or simply not travel because it would be too much of a hassle.
I can accept that the newly-extended Route 30 (UW-Kitchener-Bramalea) replaces the old Route 25F (UW-Bramalea-407) given that there's frequent service from Bramalea to Highway 407 station anyway. But they really need to bring back the 25C express from UW to Square One. I guarantee that running 1 bus per hour each on the 25 local and 25C express would generate more ridership than their current schedule with 2 local buses per hour. All while requiring fewer buses and operators thanks to the massively reduced round trip times.