the problem is people are running mono aether and as a stipple they always put 6 in. its very rare that they dont have one up after the second turn (unless you are running an EQ/quanta altering deck) at which point its feasible to always have that protection up the rest of the game (against either 30 or 35 card deck) so unless your deck has at least 6 control cards its nearly impossible to win by turn 18 out stalling their damage. dont get me wrong steal and explosion are great. but 200hp is a lot to burn. and mono aether, the only counters to the creatures are fire shield and (i believe dry spell) which takes far too long to go through 4 or 6hp. (immortals vs dragons).
in my opinion dim shield should be upped to a 7/6cost just so it cant be rushed quite as fast into the game, also so they cant play so many other aether cards like immortals and shards so quickly. i play heavy fire and 4 explosions in a 30 card deck isnt enough to handle 200hp against a mono aether deck. I love the concept of just using firelance/drain life cards to 100-0 someone in a single turn, its just not doable in arena with the HP caps.
the decks with cards like icebolt/firebolt/gas/pulverizer that do counter dim shield are very lackluster and dont work well against most other decks (rainbows, pdial, miracle, reflective shield), so i can see why some people want dim shield changed.
I would love to see a gravity/earth deck with auburn nymphs/pulverizer/gravity pull come to life and break certain decks (mono aether), but it takes quite a bit of quanta to set up.
however in terms of pvp the card is very UP due to rushes in 100hp being very possible.
overall im against the removal of the card due to it having specific counters (steal+explosion)
TL;DR in pvp its UP. arena is extremely OP or useless altogether.