I think the Mississauga Transitway is, was and always will be more underused and unproven than Sheppard. Sheppard at least had a bus before. The Mississauga Transitway does NOT have a built-in ridership, it's a completely new route with completely new stations. There was nothing there before. It's a little premature to judge it though.
The transitway did in fact have a bus before, albeit running on nearby parallel streets (on Rathburn for most of the route that corresponds to phase one, then up Tomken and onto Eastgate for the balance). There were no equivalent stops to Central Parkway and Cawthra. And up until recently, both 107 and 109 weren't even full-day-long routes, and are only recently 6 day a week, still aiming for 7.
I agree, though, it's not really a fair comparison, because the first phase corresponds to the portion of the overall route where there's the biggest displacement between the old and new corridors, and it also corresponds to the portion where there is probably always going to be the fewest boardings and alightings. As subsequent phases come online, there will be smaller shifts in bus stop locations, and those stops will have a lot more employment in walking distance.
For at least its first two decades of life, and probably for far longer, MiWay buses will use the transitway as a line-haul route, primarily moving people back and forth between MCC, the employment clusters at Eastgate&Eg and Airport Corporate Centre, and destinations off the far end (B-D subway, airport, Malton). The intermediate stops like Tomken and Cawthra were always bound to be mini-Bessarions, but the comparison ends there because:
(1) they didn't cost $100 million a pop,
(2) the overall asset cost far less, both in terms of up-front capital and ongoing lifecycle
(3) this is actually a *phased* rollout, and the rest of the line is genuinely coming. Try as some folks might, you can't just call the existing Sheppard subway "phase one"; it's a finished product, for better or for worse.
(Off-topic-aside: Guys, it's been ten years, how many more decades of whingeing from certain quarters do we have to brace ourselves for about how a billion dollar stubway would be bursting to the gills with traffic if only those snooty pinkos could find it in their hearts to spend $4 billion extending it east and west. Yes, we know, we know, every single York University student works a shift between classes at the Taco Time in Scarborough Town Centre. And, yes, we know, count all those lanes on the 401. And yes, we know, everyone coming down Yonge from York Region and getting on at Finch would like nothing more than to ride two stops, transfer over to the Spadina line, and head downtown because, you know, relief.)