Ivanhobe
The Extraordinary Fan(boy)
trying to argue Gatchaman deserves to be considered a Sentai series makes even less sense than arguments for stuff like Ninja Captor or Supaidaman.
If we go that route, we could argue that when Ishinomori came up with the concept for Sentai, he was more inspired by his own works (i.e. Cyborg 009 and Kamen Rider) than by previous existing works (Gatchaman). I think the only valid comparison we could make here is that as Sentai evolved, it did started to resemble Gatchaman, but i think that was more a thing of the times.
I personally think Dekaranger and Gekiranger are underrated due to skreetchy reds. Ban and Jan are actually stand-up guys, there for you when **** goed down with a "never-give-up" attitude.
Dekaranger is quite popular so i really doubt that is the case, but when it comes to Gekiranger i never understood why people dislike Jan so much. Personally i found his antics funny and his character arc was quite something, it really helped to make of Gekiranger the epic show that it is.