Actually, that example could also be made to work in Kate by putting cursor before the numbers.
Those are just contrived simple examples to demonstrate how multiple cursors work with paste in other popular editors which have similar feature.
Block Selection Mode will not work with irregularly shaped text not at the beginning of the line or when selected lines are not continuous.
Sublime Text was one of the first (if not the first) editors with multiple cursors editing and it had a long time to perfect it. It implements special logic for pasting when there are multiple cursors on the same number of lines. Bonus is that user doesn’t need to think if Block Selection Mode needs to be used for some operations and how. Current conversation proves that point.
Sublime Text doesn’t have separate Block Selection Mode because such feature is simplest use case for multiple cursors and it is not needed. Kate had Block Selection Mode for a very long time before introducing multiple cursors like in Sublime Text, in my humble opinion it should follow that editor with its implementation of similar feature.
In Sublime Text this:
a a
bb bb
ccc ccc
1
2
3
Can be converted to this:
a1 1a
bb2 2bb
ccc3 3ccc
But cursor movement by a word from another recent topic is also needed:
https://discuss.kde.org/t/cursor-movement-by-a-word/26126/1