Compared to what type 2-stroke?

A 4-stroke should have more resistance to being turned over than the same displacement RINGED 2-stroke. An ABC engine when cold would be harder to turn over than the 4-stroke. ( I know of no tapered sleeve ABC 4-strokes... but I haven't seen all engines out there by a long shot.)

Its qute pssible you bought a worn out engine. Its also possible it needs valve adjustment and would be fine. (Its possible its just fine as is...) You need someone familiar with 4-strokes to look at it in-person.