Chansey is a poor choice for an evasion abuser since it's weak to Terrakion's Sacred Sword, which is very usable.
She's also the perfect setup bait for CM Mewtwo with Aura Sphere -or pretty much ANYTHING with 101 subs and Aura Sphere. She's just going to waste PP without accomplishing anything.
I'm not finding evasion moves to be that broken so far TBH. Even a single turn spent using unreliable defensive moves in ubers is too risky with titans like Kyogre and Kyurem-W who can OHKO or 2HKO the entire metagame.
Hopefully, if they stay banned, the reason won't be something stupid like "we all agree evasion moves are not a viable strategy but we find them annoying so we're keeping them banned anyway".
Though I don't have high hopes for a more rational reason after seeing the comments on the OHKO clause test.