Carcassone Hills & Sheeps - how do the sheep rules make sense?
Yes,  you are missing something.

'Lucky guy' in your example gains the same benefit as 'clever guy', despite playing fewer field tiles.

Each time you place a tile and cash in the accumulated points for that field you are foregoing a chance to (maybe) increase those points. The optimal number of points accumulated before cashing in depends strongly of the distribution of tiles.