The timeline may well be different your side of the pond, but over here...
For most PayPal cardholders, eBay is literally the smallest portion of their PayPal spending.
That's true for me now, but it started completely the other way. Paypal was as trustworthy (in the sense of, would you give them access to your bank account) as Facebook Libra is now. That is, no way. It was a nothing and not missed. I had several cash cards for Internet spending, which made sure that no online store had access to my unlimited funds.
But then I was using Ebay a fair bit, and PayPal was a
lot simpler to use for payment on there. Took a while but eventually (and encouraged by Ebay) all my Ebay payments were via PayPal. But that's all. After that, and quite a lot after, since I had a PayPal account I started using it for online checkout at other places. Again, took quite a while to work up the trust and not that many big-name stores took it, but over time it crept in more and more. Ebay buying PayPal accelerated the process, and now it's my preferred payment processor online.
I doubt if I would be using PayPal so much if it weren't for Ebay, so in that sense Ebay carried PayPal forward. Now, PayPal doesn't need Ebay. Such is life