With 100 Base SpA and no invested EVs, Milotic isn't doing much damage to anything with a 120 Base Power move. The common argument is that "Milotic isn't here to sweep" but it's important to hit switch-ins like Jolteon and other special sweepers for a substantial amount of damage to prevent them from repeatedly coming in to threaten Milotic.
I'm not convinced the damage difference is enough to a sweeper care more about being hit by surf then it does about being hit by boiling water (then again I'm still working with useing her in UU while you seem to want OU so we definatly have different environments we are thinking of). Also if you manage to hit the sweeper with a Burn then the damage difference is more then covered.
Secondly, Milotic's common switch-ins don't really care about burn. Let's think about this one: who commonly comes in to force Milotic out? Grasses and electrics, of course! What do these grasses and electrics hate with a passion? Toxic!
They do care about Burn, they just don't care about their Attack being cut (well some do, like Physical Vena and Tangrowth). Burn damage is still pretty respectable especially if they switch alot (as Toxic needs 3 turns of sustained damage to equal Burn's damage, if they swap it's weakened). And no one says you can't still run toxic if you like.
Thirdly, it develops a bad habit when you try to stay in on physical threats you can't beat just to give them a burn. 30% burn rate isn't very reliable, and it can prove to be deadly if you give these physical sweepers too much of an opportunity to set up.
Lets not assume that people will play stupid just to support one side of an argument. If staying in isn't smart then people shouldn't, boiling water or no. That doesn't change anything however argument wise. Boiling water doesn't require you to sit there for multiple turns if it's not in your favor to do so.
Also, you would just be asking for things like Guts Heracross/Machamp/Nageki/Roobushin to get a burn and set up on you. That's no fun.
No worse then hitting one with Toxic (which again might be a better status for them depending on how often they switch).
Unless the damage lose is significant enough to be noticeable I still don't see the down side.
 
 
		 
 
		 
 
		 
 
		 
 
		



 
 
		



 
 
		 
 
		 
 
		