The concluding paragraph of that article summarizes it as being an issue of stop spacing. Which is not easy to fix.
You're right that Ion is slowed by some of the turns it takes very slowly- my non-expert opinion is that it could probably take some of these a bit faster, and maybe one day will. There's also a part near the end of the line with a very slow speed limit that might be able to be improved by construction a footbridge. Ion will get a little faster, in short, but how can Finch if the main difference is that it has very little opportunity to get up to speed before the next station?
On stop spacing of 6FW vs. ION,
1. Yes, stop spacing does influence average speeds
2. No, stop spacing is not the biggest factor in making 6FW slower than ION - it is by far operations
3. I don't see the turns on ION being taken much faster. I obviously do not know the exact specifications, but from my measurements they're about 25m minimum in curve radius, which is usually taken at 15-10km max with current low-floor trams. I do not know exactly how well different types of rolling stock can take them.
Boring data time form my Big Spreadsheet of Transit Data:
| Avg. Speed (kmh) | Avg. Stop Spacing (m) |
|---|
| ION, Willis Way to Mill Stn. | 17.8 | 743 |
| 6 Finch West | 13.0 | 606 |
| Paris T9 | 19.1 | 572 |
| CTrain Blue, Kerby to BVC Stn. | 14.1 | 430 |
Takeaways: These speeds mainly show a mix of infrastructure realities and operational ability. CTrain kind of pulls all the stops out to make it operate fast in the downtown core, and it shows, managing to eek out 6FW despite super short stop spacing. Even though ION has good operations and farther stop spacing, it still loses to T9 with (by Toronto standards) insane operating standards that could never fly here and less curves.
So: Stop spacing does matter. Currently, operations matter more. If operations was good, I am pretty sure stop spacing/route shape would be the next bottleneck.
(Edit: I considered TSP as part of Operations. Separately, I agree with nfitz and i'd rank Ops, then TSP, then Stop Spacing in decreasing importance.)