Hey @Florian_Bentouhami,
So first of all if you want instant redirection follow the instructions here: One click upsell hack for PayPal Plugin in Clickfunnels that should make automatic redirections from one step to another (without having to click return to merchant).
By the way the above, is only needed for PayPal Plugin v1, v2 has much faster redirection.
As for Credit Card checkout through PayPal, it really depends, if you customers make an account during their checkout then it will be kept logged in for enough time to go through your entire funnel, while if they selected to not “be remembered” or kept logged in then Paypal has nothing to do but obey what their customers want…
After all online buyers like PayPal for it’s safety, and keeping your credit card active on any device is a major security breach (if the customer wants not to).
Hope that explains the concept 
let me know if you have further questions 