They do have similar backgrounds but the LK is kinda haxxed.
Help in fights gives you a good idea of where you stand, you don't get any help to deal with Lei Shen.. whereas you needed the combination of the LK toying with you enough for him to be actually weakened by the blows, Tirion breaking out for whatever heavenly reason while disarming him and pretty much every soul inside of Frostmourne holding him down while you butcher his overconfident ass.