I wondered if the Blues may have jumped the gun with Kyrou's extension, as I felt he hadn't proved as much as Thomas had up to that point, but those concerns have been mostly addressed at this point. Thomas is the better all-around player as you said, but he doesn't have the ability to take over a game on his own like Kyrou does. They showed a stat during last night's game that only McDavid and Thompson have more points than Kyrou since the middle of November.
The biggest concern for Blues fans is would Kyrou work to become more of a complete player, but he is a lot more engaged in other areas of the ice, which is great to see. He'll never be an elite 2-way player, but I think he can be more than adequate if he keeps improving.