Am I being a sore loser and letting my ego get in the way?

I joined a small company as a senior ML lead. The product is a chat application where trained executives respond to domain specific questions using a knowldge bank. I was hired to bring in AI based suggestions and capabilities to ease the executives' workflow (not replace them).

I designed a minimal featured system to start with that can respond to 'easy' queries using stuff like intent recognition, topic detection, search and RAG on the small knowledge base. It wasn't perfect but it worked and was a huge help for the executives.

They now hired another engineer to help move faster with adding more features, but this guy turned out to be prompt engineering rocks - vibe coder type. Strongly opinionated, goes around telling everyone 'how he would have done it' for everything. Dismisses the entire system I built, proposes to put the entire chat history and knowledge bank in the prompt and convinces everyone this is a better and faster approach. I tried pointing out the flaws in this approach around explanability, scale and safety, but to no avail. The leadership is impressed by the 'simpler' approach and want to go forward with this and I'm questioning my own knowledge and the place in the company. Am I being too stubborn or just disagree and commit?

I don't know if I am even describing my situation accurately.