Of the past 20 years (1996-2006), I'd say yes.
I think people are not taking into account what impact actually means.
I think people are confusing it with most respected artist.
Her impact is evident on her generation as well as the mid 00s/late 00s generations and the current generation.
Her impact on performances, videos, pop songs is unmatched.
And this is the good stuff.
This isn't even taking into account her dark past where her impact on the pap game occurred.
When you think of school girl outfits, plastic snakes, sexy steward outfits you think of britney
When you think of tanned toned and blonde to depict the ideal look of the early/mid 00s you think Britney
Even the not so good things: lip synching, autotune, shaved head, the crotch showing so on and so forth.
You might get artist like Pink, Beyonce etc. to have many peers and following generations liked them but liking, being influenced and impacting an artist you find in people like Britney.
She's basically wrote the book on all the good bad and ugly involved in being a popstar post information internet era and closed the book on the chapter of being able to comeback and make more money post prime than during her prime.
TV shows, movies, songs have been built around song titles or her life at certain phases.
She's embedded in pop culture without having to use media propaganda to make her looking more than what she is.
The sad thing is had she been on fire in 2008 the way she is now with her confidence, energy and nailing the dance moves she might be in a better position.
2008 was a good comeback but it could have been grander had she tried after the first month and 2011 just deflated her comeback success.