400 is likely an overstatement... But in some bases the attrition rate is ~10%, so the real number wont be too far.
Mostly FOs moving to a better career in the various flag carriers currently recruiting (BA, IB ...), or headed to the sandpit (not as many as previous years), but many capts considering options as well...
Cadet level has dropped underground, as they need everybody capable of pressing MCP buttons on the line.
In any case, don't expect any improvement in conditions, that will never happen in FR, unless you consider them paying your TR and bonding you for a ~30k non-prorated after all penalties should you leave early an improvement.