Well, I don't remember Superman actually doing anything at all in the Prometheus story, haha. I do of course think Morrison likes the character and can write him well, but I don't think he was more effective than really anyone else when it comes to making Superman look like Superman in the process of doing a real League (because to be fair, the Jurgens 90s run was just built around Superman).
Superman as an idea seems to be the focus for Morrison and Johns, that's why I think we see stuff like the dozens of other Earth versions pop up from them. But when someone writes the League they typically just want to take him down quick and hard for the sake of narrative stakes and then for him to say something noble near the end. A story rewrite removing Batman is much less manageable than removing Superman, or even MM sometimes.