In many cases, your next project is more or less similar to previous ones. It would make no sense to spend a lot of time learning new tech since you already have proven solutions. But sometimes, it can be the wrong decision to make.

It can easily become your comfort zone and it can make you avoid better solutions for your current project.

It can be challenging to plan every detail of the project. 

From a product manager view you have to think about the limitations of the technology, you have to think about users who will use your product, you cannot forget about business and marketing requirements and so on.

Sometimes, some of the requirements aren't known at the beginning; sometimes business circumstances change, and sometimes you have to build something first to figure out it can be done better.

Important note: product managers make mistakes as programmers make bugs.

Instead of trying to show how wrong they are, you should focus on finding solutions.

Isn't only about technical skills, but more about to understand what is the value you can bring to the company and how to do it. 

A senior developer isn't someone who knows every aspect of the tech. It is a person who will help the company build a great product, even if this requires to cross a border of their comfort zone. Solutions over problems.