I also started this book about 10 days ago. He gets some of his info wrong, I quess from writting a book 50 years after his war experience. Patton had nothing to do with the M26 and that tank was developed about as quickly as possible according to other books I have read about it. The M26 was not the only heavy tank program the US had.
Of course the Allies are going to lose more tanks, they were attacking prepared defensives. The Tiger and Panther were better armored and higher firepower, but were a maintenance nightmare. Most M4s had more then double or tripled the hours and mileage that the German tanks, and still were running.
I think the Allies would have been slower with the M26 and M4, since they would have to carry parts and ammo for two totally different machines. They had a hard enought time keeping parts for the M4 on hand as it was.
The Allies might have been better off to get more M24 Chaffees into battle earlier. These would have helped encircle the Germans after the breakout of Operation Cobra.
If the M4 was such a bad tank, why did the US Army use it into the Korean War and other countries until the 1990s? I think Cooper bases all his opinions on see some many M4 destroyed in the Battle of Normandy. But that goes back to the Allies attacking and the German;s defending. The attackers always has more casualties.
Now if the M26 was the only tank the Allies were using, then that is a different story. They would have geared the supply operations to support only one tank, like they did with the M4. Sure it would have helped with tanks loses, but they still would have lost a lot attacking. But they use more fuel and the Allies had a hard time keeping M4 fueled up, so that might have slowed the battle across France.