Well, if you consider the Gokaiger cast purely as Super Sentai archetypes, Pink is by far the least interesting on paper. She's basically the same girly-girl that White Swan was 20 years ago and has yet to break out of that mold.
That said, White Swan is one of my all-time favorite rangers? I really like the take on the girly-girl ranger where she has girly mannerisms but has to do a lot non-girly heroic stuff because no one else can. So Pink is okay by me.
I suspect a lot of Gokai Yellow's popularity is that if you view her purely in light of Super Sentai archetypes, she's the most original and ground-breaking take on the tomboy Yellow archetype we've seen in awhile.
Now... that goes back to Nami in One Piece being a really ground-breaking character even by shounen manga standards. Sadly, shounen manga women are usually miles ahead of Super Sentai women in terms of characterization.
If you dump a character exactly like Nami into a Super Sentai team then, yeah, she's going to come off super-awesome. I could really get into Luka if she'd just do something that Nami wouldn't and restore my suspension of disbelief.
