The thing is though, facing any of the other two stats while they are buffed to the max counter balances things.
The loss of mobility that might come with high defence means you will never catch a Speed buffed opponent. And since they can juggle really well and you can be juggled really easily, they can quickly build up damage despite your defence boost.
And if you are facing a Power focused character, they simply have the extra power to neutralise your extra defence.
Then, you have character specific equipment setups which make things even more complicated and interesting.
For example, lets take a Bowser with massive defence buffs. Can survive to like 300% against a regular fighter without much problem. Cool.
Now pit him against my "Power Rosa" - Rosalina with +110 Attack, -2 Defence, -31 Speed.
This means my Rosalina can counter every single benefit of a tank Bowser. The match would be a cake walk:
-Having a totally Defence oriented Bowser means he loses out on much of his attack power. Meanwhile, my Rosalina is basically no easier to KO than normal (-2 Defence is virtually no change at all). So in hindsight, this means Rosalina is harder to KO than normal, because her defence is basically the same, but Bowser's power is greatly reduced.
-Rosalina now has absurd amounts of power to neutralise the Defence buff Bowser has.
-The Attack buffs apply to Luma. Making Rosalina's damage output and KO options even more absurd.
-The Speed reduction on Rosalina is not too bad. She's basically Mario speed. Mario can combo well in this game. Rosalina can too. So the speed reduction doesn't ruin that, since Rosalina has great range and juggle abilities regardless. And Bowser's Defence makes him even easier to do this to (and he's easy to do this to by default anyway, because he's so big and heavy). Expect Rosalina and Luma to play ping pong with Bowser and rack up that damage.
-Depending on the custom moves she uses, Rosalina can easily bypass Bowser's Defence and any "hold the fort" strategies he might use because of it. Luma Warp means she can send (an Attack buffed) Luma right behind him and easily punish any attempts at attack (Luma Warp has virtually no end lag, both Rosalina and Luma can attack out of it near instantly).
-Should Rosalina be knocked off stage, she still has an amazing recovery. However, Bowser's ability to recover has been nerfed quite a bit. Against an edge guarding master like Rosalina (who is now BETTER at said edge guarding due to buffed damage and knockback), this is most undesirable.
