Actually, that’s not really true.
Rockhold had longevity too. His streak started in Strikeforce and (apart from a lone loss to TRTor) ended after he destroyed Weidman.
He beat at least 7 highly regarded opponents over a 14 fight win streak (again, disregarding Chitor)
Not just you, but the mentality of ‘if it didn’t happen in the UFC, then it didn’t happen at all’ has always bugged me.
Their 6 best wins during their streaks (IMO)
Weidman
Machida, Belfort, Maia, Munoz, Silva twice
Rockhold
Machida, Weidman, Bisping, Kennedy, Jardine (maybe Philipou or Boetsch instead? ), Souza.
And Rockholds streak was interrupted by a guy Weidman demolished.
His win vs Weidman aside (can Weidman beat himself?), Weidman would likely beat everyone Rockhold faced. Souza would have been a test though.
We already know Rockhold didn't beat Belfort (admittedly it was a better Belfort Rockhold faced), and he probably wouldn't have beaten the Silva that Weidman faced either, but Rockhold definitely beats the rest of Weidmans competition.
and I'm definitely not this "if it didn't happen in the UFC then it didn't happen" guy as you suggest. Fedor is the GOAT in my eyes. Just because I don't believe that rockhold's Strikeforce wins outshine Weidman doesn't put me in whatever category you choose.