This may indeed be a generational thing, at least in part. I grew up on TOS, long before the latter-day shows came along. Beyond that, I grew up when movie and tv series took a much more laissez-faire approach to continuity and casting -- and "canon" was not the fannish obsession it is today.
At the risk of showing my age, I sometimes wax nostalgic for the days when we never worried about whether the latest Sinbad or Tarzan or Godzilla movie was "canon" or not. Was
Son of Frankenstein 100% consistent with the previous two Karloff movies? Not at all, but nobody ever insisted that it took place in a different "timeline." Ditto the early Bond movies. And did we demand an "in-universe" explanation for why Darrin on
Bewitched was suddenly played by a different actor? Or why Marilyn Munster was replaced -- twice? Nope.
Heck, Catwoman went from white (Julie Newmar) to black (Eartha Kitt) on the same TV series and nobody blinked an eye, or demanded that the show somehow explain or justify this.
So, yeah, April going from a white cartoon character to a black live-action guy, fifty years later, doesn't faze me.