This can turn into an advantage once you leave, though. Once you join a decent company you get very motivated to do your best, because you never want to go back.
And honestly? I don't believe Citi management knows enough to know who their bottom 5% are.
If 100 is the typical productivity of a smart person when she's making the technical calls, picking the tools, and writing a new system, most corporate environments expect software engineers to function at 5-10-- maybe 20-30 when they get to senior dev roles. The problem is that if you're used to 100+, that feels like being at 0. It's demoralizing when your productivity is a rounding error for environmental reasons that aren't your fault.
(I named it for Jack Welch, father of rank-and-yank.)
Consequently, companies tend to lay off from the middle, not bottom.