'regarded themselves' is a perfectly correct and usable phrase in written English.
You could use it in a sentence such as this: "The players regarded themselves as the best team in the league."
The men regarded themselves in part as an accountability group.
"They regarded themselves as ready and they performed as ready.
But the crucial point was how the two men regarded themselves.
Trade was often with particular partners who regarded themselves as distant relatives.
Ministers such as Bute, Grenville, Townshend, and North regarded themselves as Whigs.
In Louisiana, members of the SCAT teams regarded themselves as intelligence officers for the cleanup.
Old-family Episcopalians have traditionally regarded themselves as the nation's economic, political, and cultural elect.
It was also different when wives, whatever their own abilities, regarded themselves as second fiddles.
They regarded themselves as civic communities in which the students were the main interest group.
It is not so long since these sides regarded themselves as part of England's football elite.
Rugby union was amateur then, but Australia regarded themselves as professional in attitude.
