The rivalry continues in the fibre era, with ITU's GPON and successors competing with IEEE EPON etc. ITU does seem to have lost out comprehensively at layer 3. They do some stuff like OAM which is only interesting at Telco scale, although in the mobile era bodies like ETSI are more relevant.
The other difference from that era, and even the early internet era, is how much is no longer standardised at all, but decided by global monopolies. Back then it was a given that Everything would at least need to interoperate at the national level. But we may be returning to that .
In the US at least the fiber standards are shaking out to telco vs. cable. Fiber providers who used to be telephone companies (AT&T, Verizon, and the smaller former Bells) are hitching to ITU standards in products developed and sold by vendors who have always sold to the Bells (Nokia via Alcatel via Lucent). Many of the startup fiber providers fall into this category, too (Google Fiber, Sonic, etc--oftentimes because they started as DSL companies riding on physical last mile networks of the telephone companies)
ISPs and providers (fiber or not) that started out as cable companies (Comcast, Charter) are hitching to SCTE/CableLabs standards and equipment from their traditional vendors (Commscope, wherever Cisco's Scientific Atlanta business lines ended up)
In the US there is little need for interoperability since networks don't have to be unbundled or support any kind of competition, outside of cable networks have to allow a customer to bring their own CPE (and only for copper networks, when they move to fiber all bets are off)
The only benefit interoperability brings is pricing--if a vendor can sell their platform to many ISPs, they get an economy of scale. This doesn't mean standards win, even in the cable world in DOCSIS 4.0 there are two flavors, with Comcast being just about the only company that has picked one flavor, with the rest of the industry picking the other