Not bitcoin killer because it's still centralized and has bigger fee (for most transaction).
In this case, blockchain technology just replace or upgrade their system, that's all.
After all, VISA and bitcoin has different kind of user base.
You're missing the point.
For Bitcoin to "succeed" it needs mass adoption right?
Rather than this current fringe user base.
Hardly anyone
uses Bitcoin.
Ask 1000 randomised people, maybe 1% will have heard of it, but I would wager, none of them "use" it, or have any, or ever had any.
The big Credit Card companies could, overnight, launch their own "token", with lower fees than Bitcoin, with instant confirmations, with adherance to policies/legislation etc
and create mass adoption, leaving Bitcoin as it is, a fringe use digital currency.