Few things.
When you're in the hip hop industry you are studying and writing so much that half the time you forget what's yours, what's not, what you came up with, and what you heard last week. On top of that you're hearing music all the time subconsciously and may not even realize it. I've caught myself writing shit and then realize I was putting down something I had heard on the radio in the background the week before.
Also about the mixtapes.. It's true that alot of times artists will pay homage to other artists by flippin some of their lines or even word for word. That along with recycling beats is just one more reason why the RIAA hates mixtapes and been trying to shutdown the operation for years. Cuz everyone bites Copywritten material in some form or another.
Jay-z is a hip hop great and he's just as guilty. He's spit line for line biggie verses, as well as use verses from bambata and other legends in the 80's. but that doesn't make him any less of an artist in my mind. I honestly don't even think he was aware of it most the time.
With that being said, I'm not coming to the defense of lil wayne. Lil wayne IS faker than pleather. And anyone who knows him, grew up with him, or where he came from will be the first to tell you that. If you listen to him because you think he's a hardcore thug, then I'm sorry to break it to you. but he's not. It's all image and hype. And it sells. so it's obviously working.
and if you need more proof besides the Weezy kissing Baby video. Watch this:
But that doesn't change the fact that he makes catchy ass music, is doing his own style, and makes hit songs. so more power to him.