They should rework the way Dieties are selected vs. Cleric Domains and Paladin Oaths in general.
It doesn't make any sense that you can be a Light Domain Cleric that worships Shar or a Life Domain Cleric worshipping Bhaal.
I disagree, there's no such limitation on it in 5e, so why put it in a game. If you think it makes no sense, then you don't play it. It's as simple as that.
This isn't an MMO, your immersion isn't affected by other people's choices.
Besides, gods work in mysterious ways. Shar works in the darkness, to me that means controlling light sounds like a fitting gift from her.
Bhaal, god of murder. But what if you are the Cleric who decides who lives and who dies? Life domain makes sense.
There's always a way to twist the idea of the domain to fit any god. It's up to you how you want to role play it.
Only restriction I came across so far was Lolth Drow only being able to pick Lolth, if you want any other god you can pick the other Drow (and there's no mechanical differences).