Upgraded/base cards should not count as the same kind.

[Demongod]

Except consider how different some of them are:

EG Nova vs. Supernova--two extremely different cards.  Nova is great for quick boosts, but Supernova requires its own mark just to use it, because it's twice as powerful.

Sundial vs. upped sundial.  One is a great splasher that requires two elements while the other requires a solid source of light mana.

Yes, most upgraded cards are similar.  However, some are very different.

[Demongod]

Except here's the fun part: you'd be able to pack twice as much permanent destruction as well.  And then there's always upped pulverizer.  1 gravity quantum=GG any shield or sundial so long as they're not using bone wall.

[Demongod]

For all of those wanting 6 sundials and 6 upgraded sundials, 6 novas and 6 supernovas in our decks >.<...

[Forfeit]

Okay, lets say someone has a 30 card agrro deck. Another person has 6 sundials. 6 upgraded sundials. what, 24 turns with no attack? Can still win. Add even two dim shields. Well, that's why this idea isn't good. I like the theory, I even slightly suggeted it at one time. But really? Losing due to someone else havig tons of sheilds, there is a reason for this being OP. And your example, well, it ranks up there on the OP chart with mine as well.

[plastiqe]

No way, 6 cards per deck is more than enough ty.

[bobcamel]

6 Chrysaora, 6 Physalia, rest of a poison deck.

Nah, bad idea.

[Demongod]

Yes, because two-life critters are so overwhelmingly imbalanced!

Edit: You realize that if we were allowed to sideboard for best two-of-three matches that any poison deck would get destroyed, right?

The only reason poison or quanta denial (Seism comes to mind) is good is that the cards that counter it suck otherwise, and clutter your deck.  If you could sideboard in things like protect artifact or purify, these one-trick pony decks would be annihilated.

[Demongod]

Your example fails.  Quicksand demolishes it, and if your sundials for whatever reason get dealt with (explosion/steal/pulverizer), you'll be pounded so fast your head will spin.  There's also miracle and feral bonds which would mean you'd need to deal 100 damage in a single turn.

[Evil Hamster]

Yes. Purify sucks so bad that even with it, you're likely to lose to a poison deck.

[Forfeit]

ALL the examples you've given are OP. That's why we're disagreeing with you. Give me a now OP example, that people would actually use, i.e. no all skely, photon deck.

[plastiqe]

15 fire towers, 3 sundials and 12 fire bolts.

[Spamalot]

Yeah, putting 12 of any card in a deck would be utterly foolish, with the sole exception of Nova/Supernova.

You could make some pretty sweet speed no-pillar Rainbow decks with 6 Novas and 6 Supernovas, as long as you took Entropy mark to make up for the lack of Entropy gen. from the Supernova (or if you just didn't play any Entropy cards, you could roll with whatever mark you need).

6 Devourers/6 Pests might work, actually...you'd be generating Darkness like a madman.