Otherwise I would find it too weird that you could see when it was dark, but not when it was light.
The '40s DC comics superhero Dr. Mid-Nite was blind, but could see in perfect darkness. He invented special lenses to make it 'dark' for his eyes even during the day, and used 'blackout bombs' to create darkness in an area rendering everyone except him unable to see.
Yes, if a player wanted to say that they were naturally blind but were able to see normally as a gift from their patron, that would be cool but I wouldn't make them use an invocation for it.
I would require the invocation, but I would allow it to let a 'blind' creature 'see' in darkness, for Rule of Cool. This is definitely DM fiat territory though, not a rules answer.
For the record, I would allow devil's sight to penetrate dimness as well.
Me too. It just doesn't make sense that an ability to ignore a 'lack of light' if there is no light, but not ignore it if only some light is lacking.
People treat 'dark' as if it were a real thing, like they treat 'cold'. But temperature is just molecules vibrating, so 'heat' is low or high, but 'cold' is not 'negative vibration'; 'cold' is just 'less heat'.
'Dark' is not a thing either. There is 'bright light', 'normal light', 'low light', 'no light'. There is no such thing as 'dark' in real life. You can project light from a torch, but you cannot project 'dark' in the same way, because 'dark' is not a thing, it is just the
absence of a thing: light.
So an ability which lets you see despite a
total absence of light should work equally well despite a
partial lack of light!