Well the thing really isn't about the individual skill of players. The playstyle (meta) in each mod has changed. I only know stuff about TK, so I'll take that as an example. Tk 3 years ago was very different thank TK nowadays.
The old-school style of TK (aka one hand forward 2 turnkick) would get destroyed by an easy defensive style. Mods change when people find out new/better ways to play them.
Duelers nowadays would win old-school duelers because they play the mods better.
Simple as that imho.