Yeah, I think that's a reasonable interpretation. It also means they could use ranged attacks out of the darkness with advantage. I usually see people talking about zones of magical darkness as being like a movable fog cloud though, blocking vision through it. But darkness is a more useful spell without devil's sight if you can see out, since then if you can cast it on yourself and situate yourself somewhere far away you can make ranged attacks out of it with advantage. Devil's sight then only really helps you at close range.
Having gone back and looked at the RAW on vision and light, it says that "A heavily obscured area—such as darkness, opaque fog, or dense foliage—blocks vision entirely. A creature in a heavily obscured area effectively suffers from the blinded condition". So that sounds like, RAW, even non-magical darkness prevents being able to see out of it if you don't have darkvision, and so magical darkness would prevent seeing out of it if you don't have devil's sight.
Still, I think I prefer your interpretation, even if it does amount to a house rule.