This is true, but only because Apps Script is 16 years old and used by 850m people. This should not be the data used to guide your choice of implementation approach. 
Coda Packs have many limitations; Apps Script not so many. That said, I let the limitations (and opportunities) guide me when making the decision as to which scripting environment to choose. This drives to the heart of the requirements both technical and business requirements. It’s difficult to advise without knowing a lot about the requirements.
Two aspects of code development govern AI’s ability to generate useful code. ONE of them provides a massive advantage - apps script is well represented in public repositories on Github. With vast resources to learn from, it’s no surprise that LLMs are better trained to pop out some pretty solid Apps Script code even in the face of poorly-constructed prompts.
Coda Pack code and its SDK are sparsely represented in the public domain. However, a well-designed learner prompt can generate buildable Pack code as I demonstrated recently as an update to this post.
