Job action combos one button

[Rowde]

Couldn't this be achieved using a macro?

Nope. For one macros are locked to hard seconds. The base GCD is 2.5 and SKS can lower this further.
So for a 1-2-3 combo, to be safe you'd have to wait.3 seconds between each line, meaning the 1-2-3 would take 1 second longer on a macro than direct inputs.

Second, and I've never tried to make a battle combo macro... but I'm fairly certain that other inputs, via weaving, could break the macro entirely.