I'm sorta surprised they didn't run any earlier non FDD shows in that Sunday morning slot given they had all those episodes at their disposal (although I do see they did run some from June to September of 94 but not after that, so still a 5 year window of just FDD). But maybe that woulda seemed less likely to not be seen as reruns given how FDD looked and was shot by comparison? Did they actually run them in the mornings even while the show was still on the air BTW? Or only after?
Only after, as it was always between 5 and 6:30 PM eastern during the first-run (and early rerun) era. It did get baffling though to hear Marc plug the airtime occasionally at the end of a show. During the first seven months that FDD was on Nick's schedule, you still had reruns of DD/SSDD weeknights at 6 until Get The Picture premiered in March 1991. And IIRC they were airing just SSDD episodes for that final period, meaning that 1986-88 DD wasn't rerun for about a decade until GAS launched, and it allowed people like myself (born 1985) to witness these who just missed out as a little kid. By then, it started to really feel dated in terms of feeling like a bygone era, but it was still a guilty pleasure of mine when I was in high school. As for the brief period on weekday mornings for DD in 1994, I can't remember seeing anything older than SSDD at the time, knowing that anything pre-1989 that was a Nick original, except for Mr. Wizard, was pretty much out of the loop.
That said, its tough in kids' TV to have a long-running series even if successful. Nick Arcade was criminally neglected in terms of ending first-run production early given the constant evolution of gaming; when it left the schedule in 1997, we were well into the next generation of gaming, meaning that PlayStation, Sega Saturn, and Nintendo 64 video challenges would surely had driven the game further, and of course, there was a lot more room for different Video Zones as well.
Brainsurge/Family Brainsurge lasted a respectable for Nick three seasons, along with a blink-and-miss-it 2014 Nicktoons revival. Still, this was a decent revival that beats the Wild & Crazy Kids 2002 and My Family's Got Guts revivals.