I think it is a persistant problem with 5th edition that too much of the class content (for pretty much every class) got bolted on to the class and too little to the subclass. It leads to problems like this where if the warlock spell list was a lot narrower but the Pact lists were a lot broader we would see a set of spells that would make a lot more sense.

We also run into issues where books are released in sequence and it might make a lot of sense for a subclass to get a particular spell but as the spell was released after the subclass, no luck there.




My approach as DM is to just have the player describe the character they want to play and I can swap some stuff out as needed. So in this example a celestial warlock could pick up sunbeam, sunburst, possibly heal (depending on the other classes in play), crown of stars, conjure celestial. Even better come up with bespoke spells for the character based on what they want to do.