Griffin was smart to know that on a team with so many playmakers and stars, a guy like Joe Harris had more value at the top of the second round then Cleanthony Early or GRIII. He has a high level role player skill that translates as NBA ready for a contending team from day one.
No way to know who of the three has the best long term career, but Harris can contribute in small but meaningful way to the championship hunt this year and next, whereas the benefits of a GRIII or Early wouldn't be reaped on a team like ours until at least year 3 or 4