Downtown after work heading south on 109 Street to the High Level bridge is already very congested. I can't imagine how it would be if we attract more companies to relocate downtown, and added thousands of well paying jobs. And let's not kid ourselves; most would likely drive to and from their office. Yes, the Valley Line will help once it opens, but it's just not going to work until government encourages people to take transit rather than drive. Hence, the road and congestion tolls to discourage it.
I understand where you come from, but there are a few things to consider here:
1 - we cannot adopt severe measures like tolls base on very specific times of the day, in a single road.:
There is absolutely nowhere in Edmonton, at any given time, that has the level of congestion that justifies tollbooths. Worst case scenario you get what? 15 minutes of slow movement between 104 Ave and Calgary Trail/ Whyte Ave?
2 - There are ways to alleviate traffic without such drastic measures that are cheaper and would have much less public backlash.
It is not hard to make changes in some lanes, create some on-ways and end some left turns to discipline traffic, improve the flow and reduce travel times, all while not increasing road capacity or making it harder for people to get in or out of downtown.
Reducing the traffic coming from central, mature neighborhoods is also a very good way of improving on both sides of this equation. Being realistic, we can create good conditions for the guy in North Glenora, Westmount, Alberta Avenue, McKernan, etc... to drop their daily car commute fairly easily. Better bike infrastructure, more bus frequency, having a feeder-hub express bus model, especially to serve in the rush hours... These central neighborhoods are some of the densest and with the largest number of downtown commuters. If we take their cars out of the streets, we will have made huge progress.
Let's not kid ourselves: the people who chose to live in Allard, Summerside, Sherwood Park, etc, will never drop their cars, but we still want them to be able to come and go from downtown, especially for pleasure. If we toll the roads, we'll lose these people to the suburbs forever (and lots of business and entertainment too).
Tolls might be a good fit for the likes of London, NYC, São Paulo, Moscow, Tokyo, maybe LA and Chicago, where population density is insane, both inside and outside of downtown, but no Canadian city is at this point. Not even in the GTA or Vancouver.
3 - Some degree of extra congestion is also good for business
Congestion in downtown streets can be good for businesses in many ways. It can also be a good catalyst to further develop and densify the area.
Congested traffic moves slow, making sidewalks and bike paths safer. It also pushes people towards underground, or at least with exclusive ROW, transit (and blessed be Edmonton and our underground LRT in downtown). This, in general, will add more people walking around and moving by active transportation modes, which is inherently good for retail and hospitality.
Congested traffic also creates more demand for easy, convenient transportation and ease of mobility in general. To the original point of this whole debate, it makes downtown real estate more valuable, as it makes living close to work/entertainment more desirable. This, in turn, ends up spurring more developments, etc...
Obviously, there's a degree of congestion that becomes unbearable, and we need to prevent this from happening, but as an educated guess, Edmonton would have to triple its downtown population and workforce to even begin to worry about this.