I didn't say you need it, but it incentivized the development of those more efficient cryptocurrency technologies by providing a decentralized store of value in which the market could build trust in the interim period where proof-of-stake technologies were still being developed.
What I am saying is that perhaps proof-of-work coins actually bootstrapped proof-of-stake technologies, thus leading to more rapid development of cryptocurrency technology in general.
Sure, but in that respect Bitcoin has been redundant for years.
You may say that, but given that proof-of-stake coins should be able to easily outcompete proof-of-work coins on a purely technical basis, and yet they have not achieved that success yet in practice (although they are growing rapidly), it seems the overall market still disagrees.
You don't need Bitcoin around to do that.