I also think "having someone already in the company with X knowledge, who will be working closely enough with new hire to share it" is a huge multiplier in ramp

I also think "having someone already in the company with X knowledge, who will be working closely enough with new hire to share it" is a huge multiplier in ramp-up rate. The amount of un- or poorly-documented things in decade+ legacy systems can be a minefield, but so easily solves with a quick "Oh, X, we always do Y because Z."