All the most profitable companies I've ever worked for, which also have had the smartest engineers I've worked with, would take longer than three weeks to build

All the most profitable companies I've ever worked for, which also have had the smartest engineers I've worked with, would take longer than three weeks to build an Excel sheet import system. An engineer thinking it can be done correctly in three weeks, without bothering to know all the requirements, would be a red flag for all except the most junior of positions.