Kamen Rider Diend had the power to summon temporary copies of other Riders.
They rarely ever spoke. They were just mindless dummies.

What happen if Sixth Ranger did not exist, Would Super Sentai be success without Sixth Ranger?

Yes or no

If you say yes, Why they don't need Sixth Ranger?

If you say no, Why they need Sixth Ranger for Super Sentai?

I wish could have a ramrod-like mecha.

Well, it's kind of a self fulfilling prophecy. Sixth rangers are a source of success, but they were created to up sales and rejuvenate the toyline.

DiEnd is the secondary rider of the Rider series Decade.

Which Sentai show had the most rangers in it?

Kyoryuger.

Thanks man.

they don't necessarily need them, there are several series that are successful and never added a sixth or any extra sentai members.

extra/sixth members are definitely a ratings and toy sale booster above all else.

Yep.
I do sometimes wonder what it would have been like if Toei had a super huge budget for Gaoranger and they had all 100 Power Animals have a ranger attached to it. *shudders*