Hi thanh,
You have been busy, but what have you done here? What I see is that you have reduced loop gain progressively by adding more and more emitter degen resistance and the IM distortion has increased. Why are you surprised?
This is more a win for global feedback than a fail for emitter degen. You see, while emitter degen will linearise, decrease the gain of, and increase the bandwidth of one local stage, it will also reduce the global NFB so it is less effective at reducing distortion elsewhere which may well be more prominent that the stage you're degenerating.
In effect you are robbing the amplifier of effective global NFB and depriving the stage which most needs correction - and coming to the wrong conclusions!
Hope this helps.
Cheers,
Greg