You're right. Also, if they have to pray most of the day, how are they able to do anything else like battles or eating if there too much happening at the same time or if they are prevented from praying? What would happen? And why is it not an explored restriction that would logically make sense?
more specifically, both are a transactional relationship. deities gain power through the prayer and devotion of mortal souls. like Goku with the spirit bomb. you don't actually lose anything in the transaction, but it will go away of you stop praying and following your deities rules.
warlocks on the other hand typically lose something in the transaction. but really it's just a more traditional transaction is all. you have some patron of some power beyond mortals and they want something other than prayer because they are not divine and prayer won't help them much. most classically this is a demon giving power in exchange for a soul, but it could also be the tooth fairy in exchange for the molars of your enemies if you really wanted.
I think a cleric can choose a domain without choosing a god. They can also stop following their god without grievous consequences. Warlock patrons aren't kind to pact breakers.
Just read it? No, somehow pour gold into the pages in order to learn it.
Where is that money going? Who gets it? The guy who wrote the original, or is there a giant magic scroll guild stealing all those hard earned spellwriter's profits? Is Spellify taking it and not passing it on? I have to know!
The first thing I learned in Magick: you have to do it all by yourself. It's not a shortcut, it's not the easy way. But the reward at the end is worth it. That, and much more. And that's the truth.