Huge portions of which were virtually uninhabited (such as all the territories eventually acquired by the US), except for natives that did not submit to Spain.Um... I know size isn't everything (at least that's what my GF tells me) but Spain is the 4th largest empire ever. The Ottoman Empire is 24th. That's a huge gap.
The Ottoman Empire was a major power from the 15th century through to the 20th century. Sure it wasn't near its former power, but it was far from insignificant like Spain had largely become.
As for being like the Arabs, they are at least as different from the Arabs as the Spanish, French, and other European powers are from each other.