Comparing Kyrou and Debrincat is like comparing apples and oranges. Debrincat is a shooter, has been throughout Juniors and still today. Kyrou is and I think will be long term a balanced player that will lean more towards playmaking. He is like a poorman's Schwartz. Over the past 4 drafts, I think it is pretty evident that Bill Armstrong sides heavily on a prospect's skating ability. If Kyrou didn't have that advantage I could have seen the Blues take the gamble on Alex.
I really don't think they would have.
The Blues have never in their history drafted a skater listed at less than 5'10'' in the first three rounds. (They did draft two goalies listed at 5'9'' in the top 3 rounds in '75 and '68, and a goalie listed at 5'8'' in '71.) We know that they empirically draft fewer small players than other organizations in the upper rounds, and have heard them say publicly they have overlooked talented players (like Panarin) because they were "small."
I think there's approximately zero chance that the Blues had DeBrincat at a place on their draft board where he could have conceivably been drafted by this organization. That's not necessarily a criticism, as far as this specific set of circumstances goes. I just think it's the reality of the situation that the Blues aren't generally interested in spending a draft pick in the top 3 rounds on a guy that's under 5'10'', much less one that's listed at 5'7''.