Your list only handles how senior engineers solve problems. IMO the most important qualities of a senior engineer pertain to knowing what problems to solve, an

Your list only handles how senior engineers solve problems. IMO the most important qualities of a senior engineer pertain to knowing what problems to solve, and, at an even higher level of seniority, why those problems need solving. For example, senior-level engineers will recognize when a problem is not worth solving at all. They might know that a solution is technically possible/feasible, but they will also understand that the engineering resources (i.e. their time) can, and in fact should, be better spent elsewhere -- fixing more egregious bugs, enhancing existing features and developing new ones. To go back to what you said, being able to "dig, and dig, and dig" until they solve a problem is not what makes someone senior-level. Anyone with sufficiently high levels of dedication and stubbornness can go down rabbit hole after rabbit hole until they stumble upon something that resembles a solution. What distinguishes senior-level engineers is being able to step back and analyze the situation to determine if the rabbit holes are worth diving into.