The thing is, I think you're overrating their caliber too much. As in, I think the results are a bit more in line with their abilities than perhaps you are suggesting. I think 2022-23 was their genuinely best team, and that was the one that won a round. They've for the most part been in the "maybe win a round, maybe not" caliber. I was surprised to see even the 2020-21 team that played an entire season in the weak North Division and was shockingly upset only had a +39 GD in 56 games, then you look at the roster and it wasn't that good.
Rielly himself is somewhat symptomatic. A good, not great player that has to cosplay was a Number 1 and is often a bandaid over a fledging D group as a whole. Then there's the goaltending, already behind D groups that range from mediocre to okay and almost entirely relying on the "cross your fingers and pray" method. On an elite defensive group, someone like Rielly is a high-end #3 on a well-balanced and versatile group. Or if you are weaker on Defense, you make a big commitment on bringing in an elite goaltender to cover the gaps.