It's a little early to conclude that it will be unreliable. Waterloo has kept their service very reliable through worse conditions (though I admit service there is relatively infrequent).
The question of course is at what cost? First, yes its infrequent. When you have a train running every 10-15 minutes, having strong TSP to make sure your trains run on time is incredibly easy. The problem is standards. The Eglinton Crosstown was an EXPENSIVE project, mainly because a good chunk of the line was bored and tunneled - that already puts the price of the central section at Subway level costs, and when you take the cost of the project into account, you begin to run into problems. Immediately, any notion of headways approaching 90s that would be permitted via ATC and full grade separation is shot out the window. While in isolation we can theoretically run 90s headways between Mt. Dennis and Laird, we would also have to somehow integrate a train arriving from a surface section where even if we short turn half of the trains, the chance that the train will always arrive in a precise 90s window to uphold high frequencies is effectively null. So that's already wasted cost. Next, the existing subway network constantly has emergency shutdowns for various reasons - people walking on the tracks, someone threw something on the tracks, someone jumped over a fence, but now we have to deal with a surface section where the trains have to worry about pedestrians crossing the street and aggressive drivers forming a conga line across a red light due to traffic. This is on top of not having TSP (thanks local councillors) so the trains will casually be stopped at red lights which will absolutely lead to risks of bunching or unusual train patterns.
Now if this was a streetcar line, all of this would be fine, but remember - Prices Set Expectations. When the central section has the same cost as your generic subway line (and especially when you market your line as "Line 5"), I and everyone else have the right to expect subway level reliability and service, no less. This is further exacerbated by the planned eastern extension of the Line. A surface extension all the way to Malvern is absolutely great, until you realize that you are dealing with the Line 1 problem but exacerbated. Now some incident or delay at UTSC will have knock-on impacts and will affect the service that someone at Martin Grove will face, and this is bigger because the risk of impacts is so much larger.
Elevated lines are hideous. Even the RT is only elevated where needed and only because you cannot have heavy rail interacting with traffic if you want to keep it at subway speeds..
As someone who lives near and travels through the Golden Mile regularly I would be vehemently against Elevated lines. This is Toronto, not Chicago.
Elevated Lines just like anything else are only hideous if built that way. There are plenty of cities that have built Elevated Lines where they look perfectly find and nice: Toyko, Sydney, Montreal, Vancouver, Paris. Modern day elevated lines look absolutely nothing like NYC or Chicago. Looking at Chicago and pointing at that as an example as why Elevated Lines are hideous is the equivalent of pointing at NYC and using that as an example for why Subways are hideous and we shouldn't build them.
Paris Line 6 for Reference:
