When Britney was a child, she had just as powerful of a voice and a much better tone. (in b4 "living in the past11!!") Jessica is nothing to write home about vocally.
Oh please, shall we relive some post-2006 live performances from Jessica? Bitch is in the same boat vocally speaking, except she never had any other asset to fall back on, which probably explains her lack of any top 10 singles since Clinton was still president and Buffy The Vampire Slayer was still airing.