The suggested twist rate is to guarantee stability under all possible conditions. If you shoot well above sea level on a hot day from a very good barrel that is clean, you can use a slower twist rate and sometimes do better by doing so.
For instance: Recommended twist for one of my bullets is 1:8", but I shoot it from a 1:9" twist barrel and I am very sub-MOA at 200 yards at 3300 feet and 40F temp. At -6F I had one bullet out of 10 that keyholed, but it was from a copper fouled barrel at the end of the shooting string.
To be ideal, your twist rate would have to change with altitude, humidity, temperature, velocity, and barrel condition to be ideal. If you do not turn at the ideal rate, then a bit faster is better than a bit slower. Manufacturers tend to suggest a bit more twist than is usually needed under most conditions.
Also, a suppressor tends to improve accuracy if twisting at a slower than recommended rate, but few people risk it for fear of a baffle strike. In one instance I know about, Aguila 60-grain SniperSubsonic was keyholing from a 16" twist CZ rimfire barrel. When a miniature 5" suppressor was added, it shot as accurately as 40-grain bullets and there was no keyholing at 100 yards (and all you heard was firing pin strike and a splat on the target a bit later). This could be suppressor specific as well. A monocore baffle would seem to be the best in that regard as an object will self align in an oversize tube that has high velocity gas flowing past it. The monocore baffle gets rid of baffle strike issues as well. It is a tube with cross drilled holes in it. A crossdrilled muzzle brake that is long will have a similar effect, but less effect since gas flow escapes to the side at a higher rate than in a sealed suppressor.
In air rifles, a muzzle brake (called a muzzle flip by the Brit airgunners) will usually increase accuracy. So will a straight round tube that is centered on the bore and mounted in place of the muzzle brake. All these things use the principle of gas flow in a tube centering a round object in the tube in order to equalize pressure all around the object.
