Chansey can take physical hits while holding an eviolite? Do you understand the liability of having to depend on a single item to be OU viable? The constant threat of Knock Off and Trick is extremely prevalent in this metagame thanks to the buff and wide spread distribution. Any competent player should be mindful to keep their cleric away from potential trick/knock off users? So you plan on keeping Chansey in it's Pokeball until its all gone? Clerics are crucial members for any stall player and having to keep them in the rear in fear of Knock Off users is absurd.
But that's not even the biggest flaw in the argument.
Slyveon packs a solid 95/65/130 defensive stat spread with an incredible mono-typing in Fairy. (Resistance to Fighting, Bug, Dark and an immunity to Dragon). Sylveon has a very respectable base 110 Special Attack ; factor in the ability Pixilate + Hyper Voice and you have a cleric that possesses some offensive presence. 244 HP ev investment alongside its base 95 HP allows Sylveon to pass considerable wishes to teammates. Sylveon is crippled by Trick (but then again, what defensive Pokemon isn't) but could really care less about Knock Off. Without leftovers, Sylveon can still perform to the "t" of its cleric position. How does Chansey outdo Sylveon in any respect?
Even Blissey does better than Chansey because it isn't as Knock Off susceptible and can manage to damage certain Pokemon if it carries the appropriate move (Flamethrower, Ice Beam, Thunderbolt).
Chansey tanks better than Blissey when it comes to physical hits? My question is what business do you have leaving your Chansey in on Aegislash or Conkeldurr? That's honestly just asking the opponent to set-up on you or at least have a free turn.
I really am struggling to see how 3 foot gumball can outperform Blissey or Sylveon
Dear lord...
You understand that "Trick" as an argument is largely invalid as trick's prevalence this generation has gone down by as much as knock off's presence has gone up. Rotom-w used to almost always trick, and it was the main user. Now, Rotom-w goes Physically defensive and carries leftovers the majority of the time. The usage of megas and assault vest has neutralized trick's usage.
Then again, Chansey is the first pokemon I can think in thread that has been judged due to it's need of an item. How about AV Conk, band azumarill? For azumarill, someone even said "You wouldn't face an azumarill without a band, the calculations need that". No one argued that trick/knock off could happen there. Why? Probably because good players don't let key pokemon get tricked when they have a perfect counter in a mega.
Sylveon still is only passing a little less than 50% to most of the defensive tier. This, when coupled with coming in over rocks and possibly having to absorb an attack, makes any gain minimal. If you can get in safely while taking a wish from Blissey/Chansey, it is well known you WILL GET full HP. Sylveon is outclassed in the cleric ability. People choose it for the offensive use of Hyper Voice, I think, and perhaps the few resists (bug, fight, dark... Only two of which are common).
Blissey as an special attacker and cleric NEVER happens. Don't even PRETEND it does. She may run a serene grace set that softboils +2 attacks, but blissey simply doesn't run a special attack as a cleric. In 5th gen, blissey couldn't even KO ferrothorn with flame thrower, and it consistently does too low damage to even be threatening. You make prevent one pokemon per team from coming in, but you give opportunities to so much more who can take the special attack and allow them to set up/threaten any wish you pass. It literally just DOES NOT exist.
tl:dr Chansey absorbs hits better than blissey w/eviolite, bulk is null without. Special set doesn't happen when Blissey clerics. Sylveon can't make big enough wishes to dream of competing with these two as true clerics... Only run for some offensive mono-pressure and semi-useful resists.
Please. I'll rely on my own knowledge to keep chansey clear of threats it should never take on in the first place and use the superior cleric.