LDAP might have won over DAP, but it's still heavily based on the X.500-family of standards. Unlike SMTP (which is a completely different standard), LDAP is strongly based on DAP and other X.500 family standards.

Besides LDAP and X.509, you've got old standards that were very successful for a while. I'm perhaps a little bit too young for this, but I vaguely remember X.25 practically dominated large-scale networking, and for a while inter-network TCP/IP was often run over X.25. X.25 eventually disappeared because it was replaced by newer technology, but it didn't lose to any contemporary standard.

And if you're looking for new technology, CTAP (X.1278) is a part of the WebAuthn standard, which does seem to be winning.

I'm pretty sure there are other X-standards common in the telco industry, but even if we just look at the software industry, some ITU-T standards won out. This is not to say they weren't complex or that we didn't have simpler alternatives, but sometimes the complex standards does win out. The "worse is better" story is not always true.

The OP article is definitely wrong about this:

> “Of all the things OSI has produced, one could point to X.400 as being the most successful,

There are many OSI standards that are more successful than X.400, by the seer virtue of X.400 being an objective failure. But even putting that aside, there are X-family standards that are truly successful and ubiquitous.X.500 and X.509 are strong contenders, but the real winner is ASN.1 (the X.680/690 family, originally X.208/X.209).

ASN.1 is everywhere: It's obviously present in other ITU-T based standards like LDAP, X.509, CTAP and X.400, but it's been widely adopted outside of ITU-T in the cryptography world. PKCS standards (used for RSA, DSA, ECDSA, DH and ECDH key storage and signatures), Kerberos, S/MIME, TLS. It's also common in some common non-cryptographic protocols like SNMP and EMV (chip and pin and contactless payment for credit cards). Even if your using JOSE or COSE or SSH (which are not based on ASN.1), ASN.1-based PKCS standards are often still used for storing the keys. And this is completely ignoring all the telco standards. ASN.1 is everywhere.