An engineer who's owned a P&L. Most people who can evaluate an architecture have never owned a budget, and most people who can read a P&L can't read the code. I spent eight years as Director of Development and Operations with profit-and-loss responsibility across three departments, after fifteen years writing the software.
That changes what the advice sounds like. A recommendation arrives with the cost attached — what it does to headcount, to hosting spend, to the next eighteen months — because I have had to live with that answer from the other side of the table.
Most expensive problems I get called into were not caused by bad engineers. They were caused by a decision nobody senior enough was in the room to question. That is the job: be in the room, understand the tradeoff, and be willing to say the unpopular thing while it is still cheap to change.