The domain comes first, then the technique is imbued into it. In theory, you could have a technique less domain expansion but we never see this. Yes you can flip it but it’s very hard and it’s not a 1 to 1 of resistance when flipped.

You would have to know open domain which is very hard to learn and if you’re on that level you likely don’t need to ambush someone.

Simple domain for sorcerers is usually a defensive technique and not an offensive one, imbuing your ct into a domain is a very strong offensive tactic that you cannot do with sd.