Rihanna is a bad artist?????

Do you think Rihanna is a bad artist?, im not trying to be mean or offensive, i think shes hot and i like her music and stuff, but if you think of it, shes not original really...her 1st song i noticed from her a few years back "sos" the beat was the to song "tainted love" and she crammed her words in there and it was a hit, and then the song "umbrella" she didn't even write it? they offered it o Mary J Blige and Britney Spears, and they both turned it down and it was a huge hit BUT she didnt even write it...and NOW her new song "please don't stop the music" has a part saying "Ma Ma Se,Ma Ma Sa, Ma Ma Coo Sa" thats not even written by her its written by Michael Jackson [duh] from the song "Wanna Be Startin' Somethin'" so now what do you think??? is she a good artist since her hits aren't really written by her? did this kind of open your eyes? because i was thinking of it and shes not that great and no wonder she didn't win any grammys, and Amy Winehouse got them for song writer!!!