400 hours isn't even close to making the minimum hour requirements for an ATP...Nope... As a side note, you also don't need an ATP. A commercial Multi would be fine but It would be damn near impossible, I imagine, to get an interview at a major without one. I bet most of those 400 hour wonders at the regionals have only a Comm and get their ATP after they upgrade to the left..
First bullet from FEDEX qualifications:
https://www.pilotcredentials.com/careers/index.php?a=qualifications
Not like we will hiring for a while but used it as an example.
My buddies get their hours right seat and when they move to right seat and get the type they just add some stuff to the check and whammy, ATP with type rating.