You don't work "under a senior dev" or "architect". You should just remove that junior label now. And you are a senior as well. In fact, every developer should also be an architect.
Then you are 100% right, OpenAPI or something similar is the way to go. I hope you have more developers in your team you can talk to about this solution direction and WoW.
That whole composer story is definitely a clear situation you are the senior.