This is certainly a possible solution to help balance different mechanical subsystems within a game (martial damage vs magical effects). I still don't consider a lack of critical failure a flaw though - its a mechanism to balance a game and not just crit hits need to be balanced with crit failures.The flaw there isn't the critical fail rules, it's that casters should be forced to roll aim for placement of ranged spells just like any other character using a ranged item or missile. And on said aiming rolls, a fumble would of course be possible.
Just ask Jack, a mage from an old campaign of mine, what happens when you fumble with a fireball and it goes off inside the fireproof cloak you're wearing...
The long-distance message sent to the mage's wife shortly after: "It's OK. We've got Jack. He's in our Dustbuster...."
If you roll to place AoE it lowers the effectiveness - it is now harder to get optimal placement. If you also allow critical failure wen rolling to place AoE it lowers the effectiveness even further - you now could hit your own party. This brings magic down in effectiveness to make sure damage can compete as a viable option. Alternatively you could add criticals to damage and increase its effectiveness to compete with magic.
I find that critical failure cannot be implemented without making the game either much gimmer or much more comical (unless you brush over the failure so casually that you might as well not have bothered). Critical hits less so. Though they can still have their own comedy moments. I had a game where a possessed baker bludgeoned a PC unconscious and to the brink of death with a loaf of bread. The PC was only saved when another PC doused the baker with water, making the bread soggy and less effective. All of this from a critical hit.