Roddenberry intended for Riker/Troi to be the next drafts of the Decker and Ilia characters. Riker became much more of an ass than Decker was, but his character during TNG's first season matches what we know of Decker from TMP.
Indeed, a lot about TNG was recycled from Phase II
and other failed Roddenberry projects. Riker and Troi were a repurposed Decker and Ilia. The Picard-Riker relationship was based on the mentor-protege relationship that the older, more seasoned Kirk was meant to have with Decker. Data was a blend of Xon (unemotional being seeking to learn about emotion and understand humanity) and the title character of The Questor Tapes
(android seeking to understand his origins). The "post-atomic horror" from "Encounter at Farpoint." was a repurposing of the post-apocalyptic setting of Genesis II/Planet Earth