To those saying the flames have overachieved before, they also haven't had a roster close to this good in the post-Kipper years. IMO one of the keys has been upgrading on meh players like Stajan, Wideman, Kulak, Brouwer, Bartkowski, Stone who were all playing too much. They've replaced them with legitimately talented players like Anderson, Valimaki, Jankowki, Ryan, Kylington, etc.
Honestly, Flames just skipped a year of rebuild; then the bottom fell out.
2015: PDO fueled run to the second round of the playoffs. This team overachieved. This team got 15+ goals from Lance Bouma and Dennis Wideman, 10+ goals from Josh Jooris, Mason Raymond and David Jones. Not sure if you noticed, but most of these guys aren't even in the league anymore. They're good.
2016: PDO fueled run stops, the team gives up a tonne of scoring chances and is outplayed/coached almost every night. They suck.
2017: Coaching change, they sneak into the playoffs off the back of their top 2 forwards and top D. Goaltending stands up, and collapses in the 1st round. They're okay, they're a young team.
2018: Coaching runs its course. Depth is exposed to being overly weak. Goaltending don't stand up, even though this team doesn't give up many chances.
2019: Coaching change, one of the best coaches the Flames have had in recent memory. Team improves depth to the Nth degree, is getting reasonable goaltending from Big Ttich. Star players have taken steps forward. Matt Tkachuk rounding into an elite talent.