The question here is if FLCH is being used by some carriers for rapid descent from a high and fast profile...why?
There is nothing wrong with FLCH unless you set 00000 in the MCP window. It's very useful for intercepting the GS from above however you set a min GS intercept altitude. To restrict its use below 3000' is useless especially when some airports descend you down to 1500' to intercept the GS.
For reference FLCH commands a 2 min climb or descent. Not all descents are done at idle.
An interesting note from the 777 FCOM
Note: During a descent in VNAV SPD, the autothrottle may activate in HOLD mode and will not support stall protection
With FLCH stall protection is not offered below 100' on landing.