I am convinced that Wellington was the best battlefield commander of the Napoleonic War and he was a necessary requirement for an allied victory. I have read a few books and not one has stressed just how good he was at commanding troops from various countries and moulding them into a perfect fighting machine. How the allied army stood on that ridge and took all that Napoleon could throw at them and not crumble was truely a remarkable event.
But it was Wellington who chose the ground, it was he who believed that Blucher would come, he organised the various contingents and it was he who rode around all day keeping the troops steady. It was not just the British who looked upon Wellington as a miracle worker!
Would the allies have won had he not been in command?

Yes, he had faults, but then again who doesn't!