It might be prudent to note that "cash" has meaning in the context of electronic payment research, going all the way back to DigiCash in the 90s. That system required a trusted third party to operate, but it was still cash in the sense that it is a transfer of value, not debt. The way most payment systems operate is that they are settled at a later date (in some cash equivalent). In that sense, credit card payments as well as Venmo are layer 2 solutions.

Bitcoin has decentralized non-custodial second layers.

But if they didn't-- which would be sad-- your logic doesn't follow: Is the USD not cash because paypal exists and is widely used?

Venmo is venmo. Venmo adoption Bitcoin as a currency on their platform would not turn Bitcoin into venmo. It would just create another option for using Bitcoin-- one with it's own positive and negative trade-offs.

There is a balance. The system is not very valuable at the extremes of resource usage or limited capacity, like many other systems.

> Is the USD not cash because paypal exists and is widely used?

It would be very easy to argue that it would not be if the present mechanics of the cash system were restricted to a maximum global throughput of 3 transactions a second. But no other monetary system would actually pursue such an asinine goal on purpose except as a means of sabotage.

Which explains you.