They went 30-10-5 starting January 3rd. During that same period, the Bruins were 26-10-5.
Now...let's consider that for many of these games, the Blues were still starting who I think is possibly THE WORST starting goaltender in the league in Jake Allen. Binnington went 24-5-1 during the 2018-2019 regular season. It's pretty clear that with Binnington, the Blues would have been easily better than the Bruins during that time period.
My overall point is that this board loves talking about the Blues as if they are some "lucky" team who somehow walked into a Stanley Cup Final, but they were a great team during the second half of the year, quite possibly the very best in the league when they had a real goaltender in the net.
Discount the reality of it all you want. The fact remains that we lost and it was to a very good and very deserving team. And professional hockey players don't just decide to "not show up" for a game 7 Stanley Cup Final as is being implied.
At least we can agree on your last sentence.