It can be argued that Nas, Jay-Z, and Kanye all switched up their styles starting with their second albums, even though all of them encountered a fair amount of backlash, NONE of then have been outright disowned by Hip Hop fans/media in the manner that Nicki Minaj Has. Hell Her boss Lil Wayne went from the self proclaimed "Best Rapper Alive (

) to a syrup addicted, skateboarding, Autotune screeching alien weirdo and even HE hasn't been met the amount of criticism that Nicki has. Perhaps it is indeed like you said that she switched up too soon, but I think it's because she switched it up TOO DRAMATICALLY. Even you yourself said and posted that she had some REAL Bars to spit coming up. As an MC and artist, if of want to remain credible, you have to be able to find that balance. There's almost ZERO balance in her mainstream output. And I would honesty argue that THAT extreme lack of balance exonerates her from any top 3 Female MC list. I wouldn't put Nicki Minaj in the same class as Lauryn Hill (the GOAT female spitter) nor Lil Kim, Queen Latifah, Foxy Brown, or MC Lyte. Queen Latifah could spit, could drop a little knowledge here and there, and was well balanced. Even the ultra sexual Kim/Foxy era showed more of a dedication to actual lyricism than Nicki's average by design, spoonful of sugar raps.
Again I'm not saying that Nicki CAN'T spit, I'm just saying that since she made it big she made it a POINT to drop hella crossover, pop sugary music. She, of course has the right to this, but she's not going down as a top MC off of it nor even a moderately respectable one. She's going to be remembered about as fondly as we remember Nelly or Ja Rule (perhaps even less so) for MC's who crossed over well, but had nothing else to show for it as artists.