The answer to the first question was simple.
Sylas was the Progenitor of the Milky Way.
It was just unfortunate that he was only an F-tier. If he had been an A-tier, then he wouldn't have needed A-Grade Medley at all. Between his Progenitor status and his multi-brain quantum system, he could do this without external help.
However, Progenitor status had its limitations. Sylas couldn't just endlessly take from the world around him.
The reason A-Grade Medley was so amazing was because it was able to off-load the potential backlash.
Theoretically, there was nothing to stop Sylas from borrowing great power from his territory. The only limit was the strength of his territory itself.
But if he did so, he would likely explode into a rain of blood and gore.
It was much easier for him to use the world to suppress others than it was to add strength to himself. At least when he suppressed others, there was no bridge that needed to be formed with his body.
