What is commonly called IPsec is actually two separate protocols, IPSec itself and ISAKMP/IKE for key management.

IPSec is somewhat similar to how wireguard work actually, it relies on IPs and static encryption keys. Not too hard to configured, see for example the manual keying documentation of slackware: https://book.huihoo.com/slackware-linux-basics/html/ipsec.ht...

ISAKMP/IKE is then used on top to manage the IPsec keys and parameters. This is where a lot of the complexity comes in, tons of parameters, modes, etc. etc.

So if all you want is to secure communication between two IPs and can securely exchange key material out of bands, manually keyed IPsec is not very complicated.

IPSEC without IKE is not "similar to how wireguard works actually." Wireguard does actual key exchange and has security properties such as Forward Secrecy that you don't get using a hardcoded IPSEC symmetric key.

Also, even the IPSEC config without IKE is way more complicated than a Wireguard config, with seriously sharp edges. Just look at that config you linked to. No one should ever need to know what AH and ESP are, but if you don't you very easily can configure IPSEC in an insecure manner.

Is that your absurdly simple configuration? Can I assume the contents of that web page are where you rest your case on WireGuard's `wg.conf` vs. IPsec?