umm i got idea, let oracle choose you 3 different card?
this way you will get 15 unmoveable cards.
Yeah you'd be able to get real creative with nearly half of your deck already determined by the oracle and likely most of the rest being taken up by pillars/towers
Seriously though, if there are too many rainbows out there, just play anti-rainbow decks or even post strong anti-rainbow decks on the forums so more people start using them against arena. Rainbow decks will lose more and either people will switch or their decks will get pushed out quickly by the ones that do.
Not to mention that yes, people CAN just throw together a rainbow and add in whatever cards the oracle gives, even as dead cards..but for a deck to be really effective, ideally ALL of the cards should work together well. A deck with 5 dead cards in it won't be as strong and while it might survive in the top 500, it's unlikely to do nearly as well as one that is properly designed. Maybe better rewards for the top decks would help.
Things are already set up to encourage a certain amount of creativity though, and if people STILL don't want to, it's unlikely that any amount of rules or banned cards will really change this. Ban rainbows and they'll just move to the next most effective type of deck(and there will ALWAYS be something that is slightly more effective than others). Eliminate rainbows and it could be as simple as just making a duo out of whatever the oracle gives you + fractal + best creatures from that element + any special quanta generators etc. In any case, they will find some way to make a generic deck if they really want to.
On the other hand, for those who DO want to be creative, there are already plenty of options to do so. As an example, a couple days ago, I spun Charger as my oracle card..should be able to make something good out of that right? except that I quickly realized I had no gravity towers whatsoever. Rather than just skipping that day or going with the "lol just throw it in a rainbow" approach though, I thought about it a bit, remmebered I did have some earth pendula upgraded, and put together a duo. That deck is currently at a record of 32-1(the one loss so far coming immediately after I submitted it and while I was still testing it myself..I made a couple minor changes and it hasn't lost since)
As for SoGs, if they're that much of a problem for you, there is a simple solution: Use some permanent control. Not too hard to figure that one out. And if people start using a lot of protect artifacts to prevent that..well if they have 12 SoG and 12 PA(and probably 12 sancs as well), that's a LOT of cards in there deck used up by that which can't be used to kill you..so then you can either try to outrush them and kill before they get all their healing in play or just try to outlast them and go for deckout. At most, maybe some of these cards should be restricted so you can only use a certain number in a deck, but outright banning them is definitely overkill. Even restricting cards should only be done in cases where there is no effective counter available(or at least where the only counters that do exist are very limited or only available to one or 2 elements).
Lastly, the flaming on here(from both sides) needs to stop or else I would say one of the mods needs to just lock this thread. If you can't make an intelligent rational argument for your point of view without resorting to name-calling, comparing people to Hitler, or typing in all caps and 40 point font..chances are pretty good you've already lost the argument at that point and should just find something better to do with your time.