Agreed 100%, I worked with legacy code at different stages: 1 to 2 years: very little of structure but still velocity matters a lot, complexity is not very high

Agreed 100%, I worked with legacy code at different stages: 1 to 2 years: very little of structure but still velocity matters a lot, complexity is not very high; 2 to 5 years: first customers. copy/paste designs and complexity arise; 5 to 10 years: I observed 2 different trends, software where refactoring happened, product is still not in a very good shape but it is still ok and the others, the garbage product with millions of lines: global variables, If/then/else copy/paste design, doesn't scale, broken everytime for no obvious reasons. It's going to take years to stabilise without too much churn. So everytime I'm working on a project, I pledge managers, devs to allocate time to refactor and follow those patterns, implement unit tests etc... everytime at whatever stage, after sometime the team realizes the benefit. So yes, without a doubt, good design patterns are keys to make our dev lifes as easy as possible. And the SOLID ones are definitely my favourites.