Ah yes, nothing is better than questioning the estimate of a hypothetical user story that lacks any and all detail about the existing environment.
Like, maybe 3 weeks is quick? Maybe there is all kinds of shit you didn't even think of at all? Maybe the excel sheet has all kinds of weird non-canonical data that makes it very hard to reliably import? Maybe nobody on the team ever touched an excel spreadsheet in their life, let alone imported one?
Like.... seriously. Are you one of those people who always go "you people are idiots, I can do task XYZ in 1/3 of the time all you estimated"?
When an engineer tells you something will take 3 weeks, you listen to them.