Tarasenko has no work to do to be worth his cap hit again. He is leading the NHL in shots, has 3g, 3a in 5gp and has had additional breakaways and power moves to the slot like old Tarasenko. You don't have to value him that way but we aren't the ones trying to sell him to you. Honestly Toronto can't afford him capwise anyway.
Kyrou has the most trade value of any player in the deal right now. The Blues value him like an emerging NHL star on an amazing contract for two seasons. He is 8.103M cheaper than Marner, and let's just say for comparison's sake, none of us are grumbling about Kyrou or talking about getting rid of him.
Reilly is expiring and if he were going straight across for Tarasenko the Blues would not be adding at all. But here the Blues! are adding in the extra 1st rounder.
Because it is so transparently a Marner/Kyrou deal, the whole idea is not going to ever actually be considered in the real world, that's one of the proposal's other drawbacks.