I dont see the problem design wise. They do what they do well, and fill a niche in gameplay that offers many new strategies, I think the design of the card is great.
However, overall, I will say this game needs some balance adjustments, but the way to make those adjustments is not through nerfing a card. The game needs more cards, not the defeat of existing cards.
Now, I would see a raise in the cost of Dim shield as being an acceptable change, but I think it is secondary to adding another viable shield to aether so there are more options. Id also see adding more ways to bypass shields in other elements, or other win options.
Flat out only using mono decks to determine balance is terrible. monotime might have trouble, but a light time, or time life can deckout the dim shield chain. you can add momentum to almost any deck. impossing monoelements only is a poor way to make the case, you need to look at this card in all scenarios.
Id live to see light get a 'morale victory' of some kind, or a new form of 'honour counter' or some such. Id love to see a permanent that bypasses shields, etc.
There ar a lot more ways to fix the issues discussed here outside of crippling dim shield.
further, with new players I think dim shield teaches valuable lessons
1, no deck can beat everything
2, pack a way around shields
3, expect powerful odds stacked against you
4, think outside the box, trying only one thing will end up with you pounding your head against a wall
5, certain elements have specialties
aether may be the best at avoiding physical damage, but what has the most durability? what has the most creature control? what are other ways to win besides playing a bunch of creatures faster than the opponent, dim shield forces one to ask these questions. nerfing dimshield would reduce the impact of this card, which was designed so well, it prompts dozens of other deck ideas. dim shield, in its current form, is responsible for countless innovations inplay style and the natural development of players within the game.
dim shield in its current form promotes good design, is good design and is fundamental to the game. nerfing dim shield would harm the game on a basic underlying level,. it would create a void not easily filled by any other card. its existence all but crucial to the elements meta game.
again I say, do not nerf this wonderfully designed card.
(as for me repeating myself, so are most of the people here, not much new has been said on 30 pages or so, except for half of what I just said)