Installing some blocking or a rim joist is something I would definitely recommend. I wouldn't write it up as a defect necessarily but as poor workmanship.
The rafter ends and joist ends will twist over time and look ugly. Probably won't have any real effect unless they decide to create storage space. It is possible for the joists to twist enough to create cracks on the ceiling.
I would explain the possible consequences. Unlikely that seller will do much though.

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