Originally Posted by Fat Jolteon Bandit
That's kind of the problem right there. It could be abused way too easily. Face it, if your opponent has a Blissey, the battle essentially becomes 6 v. 5. Also, the point of pokemon is to start off with weak pokemon and level them up through the story, gradually encountering stronger pokemon. Some pokemon are weak on purpose, that's why they evolve. It's not right to try and cater to the weaker pokemon, because they're supposed to be weak. That's why Dragonite and Alakazam (among others) got seriously buffed this gen, because GameFreak caters to the strong pokemon.
Tl;dr - if you wanna use weak pokemon, play NU
Chansey is OU, your "argument" is the insane ramblings of someone who couldn't find his way out of a paper bag, and you should feel bad.
You don't have to like my idea, but I think it's a mistake to suggest that having a wall on your team is "situationally broken"... or that this ability is bad because it makes your opponent switch into a wall you might have an answer for...