In many unrelated ways, Mac OS X has just always been slow.
The first computers I ran OS X on were a Pismo Powerbook and one of the first iMacs. Both with upgraded hard drives and maxed out RAM. They were almost unusable, and we'd put classic OS back on them, a new release of OS X would come out, and repeat.
I later got a chance to use a shiny new G5. I couldn't believe how slow it felt. Same goes for the PowerBook G4. The first Intel MacBook Pro didn't feel any faster.
Somewhere around the i5, Mac OS started to feel 'okay'. But I'd always still feel blown away at how fast a similar machine felt running Windows or Linux.
But I've stuck with it ever since 2010. I remember talking about my 16", saying "It's really fast...for a Mac."