Right but "Don't kidnap/assassinate the enemy leaders" is often a good policy even when nobody will enforce that rule on you by force.

For example if your country is subject to a terror bombing campaign, it's very tempting to assassinate the one leader who had the power/respect/authority to order the attacks to start but often they're also the only leader who can order the attacks to stop

In the 1970s/1980s presumably the UK could have had IRA leaders Gerry Adams and Martin McGuinness assassinated. But it sure turned out to be useful, in the late 1990s peace process, that the IRA had identifiable, living leaders who could engage in negotiation, sign an agreement, and get the bomb makers to stop making bombs.

Russia is a regional power, though.

The definition is probably not very precise. They started a war of aggression and every other country is tiptoeing around them. Iraq was also a regional power and got a very different treatment. So the “power” line isn’t so clear.

China on the other hand doesn’t get visibly involved in almost any remote conflict and they’re obviously a (if not the) superpower.

Russia has neither industrial nor economic base to project power outside of its sphere of influence. The only reason why everyone tiptoes around them is because they’re world’s gas station that attacked world’s bread basket. And largest stockpile of nukes.

China has everything that Russia lacks and more.

When you have no power you get stomped. That “only” reason is (part of) the superpower.

China was another example of superpower “style”. Not the Russian or US “let’s invade this country” or “let’s kidnap that leader”.