Ok, this has to do with your topic that Chansey is a better pokemon then Kangaskhan. Obviously, you are forgetting about the most important aspect of pokemon: card advantage. In nearly every Situation, the person with the card advantage will win a match.
 
Sure, maybe chansey has 30 extra hitpoints, which will help it survive one more turn. so what? During those turns chansey is basing his stalling on a coin toss, and buying you more time, kangaskhan is letting you draw 2 cards a turn and giving you a 1 card advantage every turn for one energy. What a deal! He's a built in bill. So while chansey buys you more time to build up your pokemon, your opponent is also building up his. But with kangaskhan, you are given the card advantage (unless your opponent manages to play a bill each turn -- highly unlikely). His attack can come in useful if needed, but I've found that I dont use him as an offensive pokemon anyway so theres no use in worrying about that. As for his 3 card retreat, scoop up/switch works wonder. Especially with a pokemon center, discard his sole energy to re-charge. Try scooping him up, bringing out a ninetails from the bench, and terrorizing the opposing pokemon. Then place kangaskhan back on the bench, add an energy, and he's back to normal. Can you do that with a chansey? Sure, you can scoop him up, but you're losing 2 energy off the table, which puts you at yet again a card disadvantage.
 
So do you still think Chansey is a better pokemon? I guess it all depends on your deck. If your strategy is to deck your opponent, maybe chansey will do. If your strategy is to beat your opponent, kangaskhan wins this comparison hands down.
 
--PimpWilly