The point you’re getting at has come up a few times on reddit too.

The idea that the fork types differ in whether they add rules or remove them is a distraction …. the problem is that the social rules Bitcoin encodes don’t map 1:1 to protocol rules.

Whilst P2SH only “added rules” in some extremely pedantic technical sense, that’s not a useful way to think about it because it ended up breaking the actual social rule people want: “coins may not be stolen by random people”.

The specific rules that make up the scripting language and so on are all working towards implementing that social rule, so if you break the social rule whilst claiming you are still following the technical rules, you’re kind of missing the point.