Roddenberry made one star trek pilot with Nimoy, it didn't go to series, he filmed another one with Shatner, it went to series.
Most of us know that series well, and we remember whose name was at the start of the show, and whose names showed up at the end.
They got scraps because they were meant to get scraps, the stars have to carry the show, the later shows that followed were proper ensembles with all the cast names in the opening credits, the sixties were a different time.
Shatner and Nimoy where only characters to appear in all the episodes (excluding the original pilot) there were plenty of episodes that didn't have the others, did any episode truly suffer from not having Sulu in?
Were any episodes ruined because there was no Scotty that week?
Chekov didnt even start till season two, and it was season three before Deforest even got his name in the opening credits.
Roddonberry might have come up with the idea, but it was other writers and producers that came up with many of the best episodes and concepts.
Shatner did not write some lyrics to the star trek theme (lyrics that were never even used) so that he could claim half the ownership of the tune, and get half the residuals every time it was played rather than the whole thing going to Alexander Courage, that was Rod.