I have always treated spells as being chargen and customization resources.
If you want to RP a cleric that is defined in part by a particular selection of spells based around a theme, I don't think anything stops you from doing so with the possible exception of a lack of suitable spells providing for that theme.
When I give an answer like that, typically I get a response like, "But the temptation to depart from your theme and choose spells based solely on utility is too great."
To which I respond, "If that is true, them you really didn't want to play a cleric defined by a particular selection of spells based around a theme in the first place."
I think 3e was mostly on the right track with it's customizable Domain selections. They were super generic and not very intrusive. I've made several tweaks to the cleric in 3e, but mostly revolving around things that pull the cleric down from being a Tier 1 character class so as to improve balance between casters and non-casters. One of those tweaks, not really intended to support themes per se, is that clerics only have a limited number of spells known and not access to every spell on the cleric list. This makes Domain selections for the cleric far more important in and of itself, without changing anything else, which in turn makes two clerics with different deities feel rather different and allows players to make them as different and thematic as they want without constraining players with other goals.
I know but I'm talking about explicit wizard spells. Clerics lobbing fire ball for example.
Well, that's not really a goal that I'm intending to support.