The best way to lower the cognitive load is to break things into pieces that make sense. I can't tell you how many times that just moving part of just a function out of the function solved like 3 or 4 problems that were otherwise difficult. And the bigger the piece that you're working on, the more true that is. The job of the lead/architect is to make sure that the system stays maintainable, even if they can't personally build every piece. And part of that is taking the people on the team and getting them to where they need to be technically to do that. And actually a great way to do that is to break the system up into simple pieces and give them to people to work on in isolation. The hard part is a lot of people don't grok isolation, so they try to drag in unrelated stuff out of habit.