That's not entirely accurate. At 11th level they start the very beginning of the Masters of the Realm tier. That tier affects countries and even the world. That last part, plus the name of the tier imply that it's the higher levels of that tier that start impacting the world. Those higher levels lead into the Masters of the World tier, where their actions affect the world and perhaps beyond.
11th level would be mid level and it wouldn't be until 13th or so that they reach high levels and really start affecting the world.
That's why I stated it the way I did.
At level 11th level, you get access to high level stuff. But you aren't considered high level until much later. 6th level spells are big but you only have that and only 1 of it.
At level 11th, you might be known around the world and might be able to do things only a handful can. But you aren't a worldshaking force, not on your own.
Much like sports, you can have high level talent and be in the pros but not be considered a star or top level talent.