Is "promoting a key" a part of deleting internal node key in B+ Tree?
I'd not attach too much importance to such kind of boundary cases: both solutions here are valid according to the definition of B+-Tree and depending on the order of operations, it is very common that B-Trees have different shapes for the same data.  Here the difference between the two results is just the one between $&lt;$ and $\leq$ in some condition and the choice is not imposed by an invariant of the data structure.

It seems to have a drastically different result because the tree is so close to be as sparse as possible and so close to be collapsible -- at most two more deletions will trigger that.  The reason is not that trees close to the boundary are typical, it is because making readable pictures is easier in that case, in practice the number of buckets per node is greater than 4 and fewer nodes are just half-full. Being able to steal one element from the neighbor is more typical than having to merge with it.

Obviously if you know something about the patterns of insertion and deletions, you may prefer one version over other, but it will be a second order effect.