My thoughts about perish song in 1v1 first of all is that
perish song was designed and balanced around the fact that a pokemon can switch as counterplay, and there is no switching in 1v1.
Secondly, strategies like toxic stall exist, were accepted, viable, and reasonably beatable. Perish song stall is like a slap to the face to those strategies. Why wait 5+ turns for toxic to kill a poke (not considering healing or curing the toxic) when you can end the battle in 3 turns no matter what?
And using protect, it leaves the perish song user open to take 2 hits total, or sometimes open to take 1 hit total, as seen here
http://replay.pokemonshowdown.com/1v1-180893242.
How many pokes and sets can take out a bulky stall poke with 2 hits, and is that supposed to be expected of you?
In my opinion, no, because that limits the choices of pokes and strategies you can use in the meta to a small pool of choices.
Now you could tell a 1v1 player to use taunt, but that already limits the player to a set of few good choices. And perish song really needs to be considered when making a 1v1 poke or team, because it's not fun at all to lose to it. Now suppose you made a poke with taunt, as a counter to perish song, how viable is it against the opponents other 2 pokes? Or against an opponent not using perish song?
Now suppose you have made a good team with a taunt user and you picked the taunt user against the perish song user, but wait, the perish song user has Magic Coat (meloetta), and now you are back to square one.
This strategy (magic coat meloetta) is of course also counterable, you could use an imprison + trick room set, but that is also very useless against other pokes. This strat can also backfire, as seen here
http://replay.pokemonshowdown.com/1v1-212410113.
Now suppose you're using a poke with taunt and your opponent is azumarill with protect, perish song, and dive. If you don't have an attack or some sort of damage to KO the azumarill before your taunt runs out of pp, you still lose. Because since protect has higher priority than taunt, you use 2 taunts for each time the taunt runs out, and protect has 16 pp, 16 x 2 = 32 , which is taunts pp. That means, even if you use taunt, you need something that deals enough damage even against the invulnerable turn of dive + leftovers/sitrus berry recovery. You could of course risk
not taunting to waste protects pp, but that is a huge risk that could result in you instantly losing the battle. Example replay here
http://replay.pokemonshowdown.com/1v1-235003904.
This further limits your choices for a viable taunt user.
Just because something is counterable doesn't mean it's healthy to keep in a meta.
My third point is something I mentioned earlier, it's just not fun. It's not fun to go into a battle that ends in 3 turns and you lose because you're faster, and it doesn't feel fair at all.