I feel like a heretic for not knowing what sam was until reading this
Be happy then as you're going to learn quite a few things on that path!
I have never used Vim in the manner you show in the Vim example. I use ex commands seldom — usually when I need to make mass changes to a file. You are really doing things the hard way if you use an ex command to add a semicolon at the end of a line.
Of course the examples I gave are easier done interactively, rather than using ex commands. I used them because they're easy to read and understand.
I do however use ex (well, sam in my case ) commands quite often though. Examples include renaming variables, changing file paths reference, fixing repetitive typos, ...
There is another area where vis does a really good job: it's a good replacement for vim macros.
Sam's x command let me select a pattern that will match amongst multiple lines, and will then create a new cursor for every match. I can then interactively change text from all these positions at the same time, and the changes apply in real time. With vim you would have to build a macro, then apply it to multiple lines and verify the result, to either undo and restart from scratch, or "accept" the changes. It's very tedious when you figure out how simpler multi cursors are.