Good point. AES hardware acceleration makes a massive difference. It's why ZeroTier 2.x will use AES. Tiny boxes that lack HW acceleration are generally not used in cases where they're pushing enough bandwidth to matter anyway.
No, but boxes who lack hardware acceleration might care about battery life.
How many 32-bit ARM phones without AES units are there still around?
i did test it. in my setup we couldn't get IPsec to not drop a lotmof packages, so the benefits of aes-ni was lost in retries. switching that IPsec setup to chacha20-poly1305 actually made most of the drops go away.
I have no idea what was going on, but wireguard and IPsec was comparable in that test, with ispec being sliiiightly faster. the network has almost no latency, so if the retries remain on slower networks, that would change.
I did not test IPSec vs WireGuard, but scp from/to my home router/NAS is about three times faster with AES (used by IPSec) than with Chacha20 (used by WG).