Which proponents? I think most people with a lick of common sense understand that a few extra hundred feet of runway isn't going to result in 777s using YTZ.
The push for extra runway is because the addition increases the range of the narrowbodies that use that airport today. That allows for more destinations. It may allow a few more airframe types. But there won't be any large aircraft showing up.
This focus on tech instead of objective noise standards isn't helping your cause at all. Can you actually tell the difference in noise level between a Q400 with turboprop and an A220 with a high bypass turbofan? The "No jets" argument was supposed to be a proxy for larger aircraft. It's now becoming an identifier for luddism and NIMBYism. Under the current logic, the RCAF could base C130s at Billy Bishop because they aren't "jets" as per the current bizarre definitions. I highly doubt anybody would think those are better than an A220.
More broadly, I said earlier, you can't expect the broader public to accept that infrastructure should be underutilized just because a few folks in the vicinity of said infrastructure don't like it. Imagine the same argument for a GO Corridor. The only realistic way to get YTZ closed is to build a real alternative. An alternative that would take share from a majority of the flights (to Ottawa and Montreal).