I have worked with PHP in my early days (2006...), for about 6 years. I wanted to move to a language more structured. When I switched to Python I felt it was worth my investment. Working as a web developer, JavaScript was always there and I could not change that. After working with Python for 11 years, I felt if I attempt to be a founder again, I needed two things from a language - structure in developing my ideas, peace of mind to take a product to users' hands. I was OK to learn syntax, but I can not become a legendary developer with magical knowledge of some language.
Refactoring the codebase is wildly different since I get so much support from the compiler/type system. And, if it compiles, it will simply not have a class of errors.
The investment is steep, really steep. I am no distinguished engineer, just another one with average talent. I have been working full-time building my product and I am preparing to launch - multiple products in the next 6-7 months, all on the same core code-base in Rust. I have never felt a language could give me this much.