I liken learning songs of others as akin to being an apprentice for a trade. Many guitar players I've known learn how to play a little. Understood barre chords and then declared themselves songwriters. Bad songwriters too. It's easy to say that you only write your own stuff, specifically if you're not good at it. It's actually very hard to learn the song of another person because it requires a specific sense of discipline.

To the apprentice example, would you want a carpenter to tell you when building your house that he/she decided not to apprentice with the skill because they had their own ideas? I'm sure, no.

Learning songs broadens your horizon to different ways to structure riffs, learn a wide variety of licks and about song structure. I think it builds up a toolbox of useful skills.

Without all that, songs will likely be an uninteresting mash of verse/chorus/verse/bridge/chorus/outro. No dynamic.