Sigh. As we have said repeatedly - the story origin mechanic predates both Genasi and SCAG. Bringing up a corner case that isn't broken doesn't justify removing the rule because it doesn't address the reasons for the rule:
Story origins exist to prevent POTENTIALLY broken combinations that MAY OCCUR when multiple rules sources are combined.
The fact that no such combinations have occurred YET does not change the fact that they might still occur in the FUTURE. In fact, with each new product released, the odds of this occurring increase exponentially.
Your argument regarding EEPC + SCAG is only relevant to discussions that mixing those two rules sources does not result in broken combinations. It does nothing to prove that mixing either/both rules sources with another (unreleased) rules source won't create a broken combo. For all we know, mixing EEPC races + Curse of Strahd material might create the first broken combo.
I should also point out that there are already a few combos that border on broken already and it wouldn't take much to tip them over the edge and these combos are from the PHB alone. The most powerful example I know of personally is one I am using myself in order to test its limits in a controlled fashion.
Moon Druid 2 / Bear totem Barbarian 5 + Sentinel feat. This combo gives you a dire wolf with extra attack, unarmored defense, sentinel, rage and resist all except psychic. At Druid 6/Barb 5 this combo gives you a giant elk with extra attack, bear rage and sentinel.
Add an insignia of claws from a season 1 adventure and your attacks are also magical even at low levels (before you hit Druid 6).
It it wouldn't take much to completely break this combo and while EEPC + SCAG don't add anything to it, future content is likely to (Esp when combined with multiple rules sources and not just PHB + one rules source)