That's not true at all in some cases it's actually the other way around entry level xeons are failed i5/7's that can't turbo boost as high.

There were only a few xeons that were made into desktop processors and they ended up as i3's there were a few of those that supported ECC.

The 'E' edition CPU's can potentially be xeons but then they aren't failed ones but highly cherry picked ones as they boot and overclock very high.