The ION also does the signal priority right. Why is the ION does everything right but the TTC isn't, when the TTC has been operating a much bigger network and supposed to be more experienced?
I think that actually, the lack of experience running rail transit in the Region of Waterloo, and a more consensus-based data oriented Regional government, are the two reasons why the ION is good. Since Regional Council didn't really know how to build or operate light rail transit they put out RFIs to the private sector to help them do so. Thus, because the Region went into the project with an open mind, they actually listened to the experts from Europe who responded to the RFI. Hiring them as part of the consortium who built (and now operates) the train.
Keolis was a big part of the design, build, and operations for the line, their first Light Rail project in North America. Keolis has lots of experience building light rail in Europe. So, when the Region asked them to design a good LRT, they just put Transit Signal Priority into the project from day one because that's what you do in Europe, and the Region didn't object because they understood the benefits. For the Region of Waterloo, they knew that they wanted a good LRT, because so much was riding on this project being successful. So at each stage of the process, the focus from all stakeholders (Regional Council, local council, Regional Staff, the consortium, even the public) was "how do we make this thing great?" and wouldn't you know it they put thoughts to paper and did it. The goal with the ION was always to be a shining example of what Waterloo can do, so eyes were on the project the entire time making sure the Region squeezed every little benefit they could out of the system.
Toronto on the other hand never really spoke with any experts around what
good light rail transit is, applied existing assumptions from the streetcar network to Finch West without realizing that it is this conservative "we've always done things this way" line of thinking that made this mess (and is why the Spadina and St. Clair streetcars suck). Transit Signal Priority was included in the design for Finch West's build but was never included in the operational contracts signed between Metrolinx and the TTC. So the TTC and Toronto Transportation did what they always do and half-assed something together that's operationally slow and inefficient but is the "easiest" option without getting council involved. Council was also MIA pretty much throughout this entire process and didn't understand any of the attributes that make a LRT good, Waterloo Region Council was involved and educated by experts at each stage of the process and they ensured that the final product was delivered to spec.
We could learn a lot from the Region of Waterloo. Over there improving transit is just something Regional Staff are allowed to do on their own. Council just approves a transit masterplan for the decade and leaves implementation details up to the experts (Staff). The City of Toronto has politicians who know nothing meddling and stalling at every stage.