Roger didn't have all these powerful people on his side, and he reigned Supreme. It was his Era after Rocks died and it remained that way until his death. That's because he had the strength to back it up. Just like how when Roger died Whitebeard reigned supreme as the unofficial King of the Seas, and that was also due to him having the strength to back it up.
He didnt "reign" anything after taking the title that he wasnt "reigning" before it.
Literally, nothing changed except giving himself a title he made up.
Strength to back up what? Being taken by your navigator to Raftel or having Oden to read PGs for you?
Which of those is strength backing up? Where is this PK being strength achievement coming from?
If you dont have the strength to back it up, someone will come along and snatch the precious title away from you?
got folks who think that a villain that is taken out by the end of this arc is/will be the peak of strength in this manga
utter rubbish
utter rubbish