This is relative. Density where? In the cities, in the whole area covered by the rail line?
Terminal stations, as per Ellis Don plans, would be in the densest areas of Calgary and Edmonton. A total population of about 3.5~4M people between the two cities is also not negligible (reminder that this is a 9 year project from breaking ground to operation. With 20 years into operations, population could be very well closing in to 5M in the corridor)
All issues considered, Edmonton and Calgary central areas are quite walkable and, let's face it, these are the two main nodes. Also, at least in Edmonton, the plan is to have a Southside station connected into a ToD.
Lack of 'last mile (or five or ten in our case) connections or amenities
Connecting to the LRT in Edmonton and C-Train in Calgary, both airports and having the stations in major transit nodes is part of the plan. Not to mention the already listed busses, car-share options, e-bikes, rideshare services, taxis, etc...
Lack of centralization of employment
This doesn't mean much, especially with Edmonton's population growing rapidly in the south and both Calgary and Edmonton making a push for densification around transit nodes, not necessarily only the Downtowns. As long as the major employment and residency nodes are connected to rapid transit, it doesn't matter.
We should've stayed with wagons and horses, then, should we? Actually, we had trains replace that, didn't we? and then cars? What makes it so impossible to create this habit, over time? No one is claiming (or projecting) that it will happen overnight.
300km on a flat, straight line is not a significant barrier
What is it that makes individual cars so much better for winter? I dare you come up with a reasonable, technical argument for that, substantiated with facts.
It's simply not convenient enough, perception of safety issues continues to push many away and to be honest with you, many simply prefer their private vehicle because they can.
What is not convenient about parking your car in a park-and-ride (or hopping on the LRT) and jumping on a fast, reliable and comfortable train, with your hands and attention free to do whatever you want, get to your destination fast and reliably on time?
What is so much safer about cars? Are they less prone to accidents (winter or not)? Are they less likely to be targets for break ins?
I'm a walker first, transit user second. . . driver third and would absolutely love more viable mass transit, but it very much is an uphill battle.
I am sorry if this is hard to believe, based on your positioning regarding many things related to the transit/bikes/waking vs cars issue