There are a lot of factual problems with this.
Space Quest got plenty of marketing and support. Anybody who remembers Sierra games almost always rattles off King’s Quest, then Space Quest (and Leisure Suit Larry).
King’s Quest was the flag ship. It sold more. It appealed to a wider base. Comedy in general is harder to get mass appeal. But this doesn’t mean Space Quest was not a money maker. Space Quest got 6 games. Aside from King’s Quest, only Leisure Suit Larry got as many. You don’t do that if the games aren’t making money. When Sierra first jumped to use professional musicians, King’s Quest 4 got William Goldstein, and Ken Williams got Supertramp drummer Bob Siebenberg for Space Quest 3. When Scott and Mark wanted Gary Owens for narrator for Space Quest 4, Sierra was on board and agreed instead of putting up a fight.
Also, most Sierra games outsold LucasArts by magnitudes. The LucasArts guys have stated their constant frustration that Sierra constantly outsold them by so much.
Ignoring the salient point that Scott and Mark could have never created Space Quest without Ken and Sierra, this could have never been a LucasArts game. The LucasArts guys have stated in interviews they hated the things Space Quest did. (They didn’t name Space Quest, but some Sierra game, but they remembered vague things about dying all the time, like picking up a piece of glass and cutting themselves and dying instantly which they hated. I think they were (mis)remembering Space Quest 3 picking up the sheet metal at the beginning. They felt that the authors were sadistic that hated the player and wanted to kill them.) This led them to things like the no-death policy. Ironically, it was probably Space Quest that help make LucasArts what they became.