XDP, in its intended configuration, passes pointers to packets still on the driver DMA rings (or whatever) directly to BPF code, which can modify packets and forward them to other devices, bypassing the kernel stack completely. You can XDP_PASS a packet if you'd like it to hit the kernel, creating an skbuff, and bouncing it through all the kernel's network stack code, but the idea is that you don't want to do that; if you do, just use TC BPF, which is equivalently powerful and more flexible.
XDP reads the data in the normal NAPI kernel way, integrating with the IRQ system etc., which might or might not be desirable depending on your use case.
Then if you want to forward it to userland, you still need to write the data to a ring buffer, with your userland process polling it, at which point it's more akin to using io_uring.
It's mostly useful if you can write your entire logic in your eBPF program without going through userland, so it's nice for various tracing applications, filters or security checks, but that's about it as far as I can tell.
