Since I had nothing better to do, I decided to look through all the Pokémon by tier, and unless I missed something, there are only 6 NFE mons tiered NU or higher (Chansey, Gligar, Porygon 2, Sneasel, Rhydon, and Scyther). So if you want a team with 6 viable mons, you don't have a whole lot of options. I suspect a lot of people will choose to use good mons despite their subpar pre-evos and give those pre-evos stuff like toxic/hazards/foul play/seismic toss. Also, I'm not sure the Chansey line is a notable threat, since having Chansey means you only get two evolutionary lines instead of three, and also means you're likely to be destroyed by any physical set-up sweeper that has good coverage against your second evolutionary line.