I’d like to disagree a bit here. I think FLAT and STRUCTURED formats + TDS + our own TDOs are covering different needs.
For example, within HiGHmed, we use TDS/TDD for data integration with Intersystems Ensemble and Mapforce
FLAT FORMAT has become quite handy for some app development and is used in multiple low-code tools like the ones provided by Better and Solid Clouds
We were able to build a full AQL query editor using our DTO model (+ AQL parser) and some more applications which require some stronger focus on backend processing.
Long story short: I don’t think there can be one single perfect format that will make everybody happy to develop software. Having the openEHR RM and Templates allows to make flexible transformations and tweaks to serve different needs.
Surely the openAPI approach would complement this by enabling some convenient support in multiple language. Hence, I think the situation has drastically improved since 2013 and an average developer is able to have their first “hello world” app up and running within 1-2 days. Not saying we cannot further improve but this is more about open educational resources and not the available tooling.