It worked for John Browning too; that's why none of his big autoloaders had a thumb safety until he bodged one in for Colt when they were pursuing the new Army pistol contract and the US Army decided they wanted a thumb safety. Earlier designs just had a "half cock" position.
While it appears that Browning felt a grip safety was enough (based on his earlier designs) the ARMY, and specifically the Cavalry (which was still at that time the prestige arm of the Army) felt it was needed.
The concern was that a mounted man, possibly moving at speed might need to reholster his pistol, with it loaded or partially loaded. HE has only one hand to do that, the gun is cocked and he is holding the pistol which negates the grip safety function.
Sure, the smart guy will take his finger off the trigger, but without a manual safety engaged, trying to shove a loaded cocked pistol into a holster while riding a galloping horse is just asking for trouble. The original term for the thumb safety was "Safety Lock", (because that's what it did, it locked the gun on safe) and Army manuals in the 1970s still used that name as the part name.
The requirement was not only reasonable, it made good sense, and Browning wasn't an Austrian engineer who thought his product was perfection, he was an American who recognized that, if it was what the customer wanted, it was what he would build, and redesigned his original prototype to include the safety lock (aka thumb safety).
I was a Small Arms Repairman in the Army in the mid 70s. The 1911A1 was still the standard service pistol. GI spec pistols and GI spec parts don't need fitting. Any part that doesn't "drop in and function" doesn't get fitted, it gets tossed and a different part installed, and, if necessary (a very rare thing) the process is repeated until you get a part from the bin that does drop in and work. Guns and parts not made to the GI specs can be anything and fitting can be required.
Still waiting for an answer about where you put your hand so that an AR safety lever (either side) digs into your hand during recoil. I wear a size 9 glove, and the lever is no where near my hand when I am shooting.