This is just not true, people get promoted for delivering impact whether the solution is complex or simple. The best engineer I know who can work with huge complex systems in a big company usually starts with a complex solution then after he understands what he wants to achieve thinks backwards and reimplements it in the fewest possible lines of code change with the already complex system.
Every large company has a ladder for promotions that includes many words that basically come down to "complex." "Drive a year long initiative" or "multiple teams" or "large complex task with multiple components" are all examples I've seen.