play more defensively with your general
Keeping the opposing general 6 columns away and surrounded doesn’t help against direct damage.
every faction has broken stuff
Yep, I don’t like the broken stuff, but we’re stuck with what the game designers chose. However, most of the broken stuff (a) involves lots of interaction, and (b) ends the match quickly. Concealing Shroud does neither.
Varaix which doesn’t have a counter
There a bajillion counters. Just about every match in which I land turn 3 Varaix still manages to be different.
You’re just too unlucky to draw any answer
Ephemeral Shroud is the only answer to Concealing Shroud in an Abyssian deck, and I didn’t draw it. (Ok, I could also run Lightbenders for a total of six dispel in an aggro deck, but I have none.) Most of the broken top-tier strategies have numerous successful counter-strategies; Concealing Shroud has exactly one.
2 mana to avoid damage for 1 turn, but without developing a board, healing, clearing, or dealing damage
2 mana is hardly enough to hinder significant damage-dealing in turns 3-5 (as demonstrated by my opponent). You don’t have to care about anything except direct damage when you’re going to kill your opponent before you run out of Concealing Shrouds.
A weakness of ramping Variax is that you use a good chunk of your hand to do it
It only requires two cards over a normal Abyssian ramp - Variax and a single Darkfire Sacrifice. I had 3 cards in hand on turns 4-6 and replaced every single turn of the match, but I wasn’t lucky enough to draw the single answer to Concealing Shroud.