What's the problem with SoFo? The neutral cost. Personally, I think that the shards' costs don't matter that much, it's just that smaller costs are usable in mono decks and cards with larger costs fit well into a rainbow. As a consequence, you cannot balance a shard by increasing it's neutral cost, because this will only make people use it with novas and rainbows, which is silly. Shards should be paid with a low cost, enough to give it a "cost" and still become good in monos. The main problem here is that SoFo does too much as a shard: it's effects mean that it should have a very high cost, but this cannot be done because increasing the cost will only make it favor rainbows and become unusable in mono-gravity decks. This should be the same with the other shards.
TL;DR: We cannot make a powerful shard with a high cost. SoFo completely disobeys this.