So they are lazy wizards?!
They aren't lazy, so much as wizards had to really work at it to learn how to do it.
Some people can draw exquisitely just by looking at things and putting pencil to paper. Others have to take classes on art, learn about form, color, shadow and so on. They can become just as good if not better than the one granted their skill naturally... and truth be told will probably have a much wider range of styles known to them because of all the study about the history of art... but it does take a lot more work to get there.
Same thing with Arcana clerics and wizards. The Arcana cleric was gifted their magic from the deity (who felt this particular person warranted being a magical being). Other folks who weren't given this boon had to decide "I want to use magic!" and then go find mentors and books and classes in order to learn. And most likely part of their lessons involve learning about the deity of magic, what the deity looks for, and following those lessons in order to increase their skill and power (since the arcane power comes from the deity of magic). Thus they are both beholden to the deity of magic they serve.
This is unlike, say, the sorcerers, who most likely have little to no connection to the deity of magic whatsoever. They just
have arcane magic for whatever reason. Either they are descended from the massive arcane fonts of power known as "dragons"... or they just tap into the Weave somehow in a way that no one can explain and for which they've never really learned how, which is why things go a little crazy occasionally when they do (the wild mages).