Your buyout numbers aren't accurate.
Here is the cap breakdown for a Krug buyout this summer:
2024/25: $333,333
2025/26: $2,333,333
2026/27: $2,333,333
2027/28: $2,333,333
2028/29: $2,333,333
2029/30: $2,333,333
The benefit to a Krug buyout has always been heavily weighted to freeing up cap space from 2022/23 through 2024/25. Those were the 3 years where you could have cleared up $6M+ of cap space with a buyout. A buyout in those years made sense if you were truly contending at that point and could stomach to pay tons of money to get rid of him and then use that cap space to bring in a guy that gets you over the top.
Obviously that didn't happen and I don't think anyone here believes that we are on track to be a contender next year if only we can get rid of Krug and gain $6.167M in cap space. Barring a couple massive franchise altering moves, it just doesn't make sense to tack on 3 more years of (smaller) cap hits for Krug this summer by buying him out. I think there are very few potential circumstances where we would 'need' that cap space to either turn things around for 2024/25 or acquire an expensive guy who is part of the long term solution.
However, retention makes a lot of sense.
50% retention means we would pay Krug $10.5M over 3 years not to play here vs paying him $14M over 6 years not to play here. That's a big enough gap in total dollars that I don't think that the benefit of delaying payments would save the Blues money in the long run.
But the big benefit is future cap space. Retention gets his contract fully off the books 3 years sooner than a buyout. I think that is well worth the "extra" cap hits from 2024/25 through 2026/27 (assuming 50% retention). Even better if you can move him in a deal with less than 50% retention.
I do wonder if there is a deal to be made with Detroit if they don't can't extend Ghost. Krug with $2M(ish) retained could fill that need and we probably have the ability to take one of their not-so-great contracts that has 1 year left in order to give them flexibility this year.