Ehh your point is valid... it is absolutely true. However I would say 50 had a great 5 year run. Its kind of saying mohammed ali, or george foreman, or evander holyfield failed for whatever reason... when really they didnt they had their time and then time moved past them.
I mean at this point only people who legitimately have had a longer run than 5 is probably jay-z, maybe LL, maybe Drake, maybe Kanye... and none of them were as completely dominant at their peak as 50...
and thats out of all rappers EVER there are like probably at least 500 major label rappers during the last 35 years... and 50 is in the top 5 as far as a commercial run... how is that a fail?
everyone becomes the chilites at some point