What a can of worms.
May I start by saying that the people least qualified to write SOPs are the manufacturers. They do not operate a fleet of aircraft in revenue service; they will not gain experience over a period of time of doing so; they are primarily in the 'welding and wiring' business, not in the business of managing an air operation; they have no first-hand knowledge of the nature of the operation or the operators (pilots) involved, and they sell their aircraft to operators of widely varying cultures.
Whilst, for example, US operators insist upon qualifying their First Officers to a lower standard than their commanders, I accept that their SOPs might best reflect this. However, when the manufacturer writes SOPs to provide for an under-competent First Officer, and these are blindly adopted by operators elsewhere who qualify both flight deck crew members to the same standard, then the SOPs are effectively 'dumbing down' the operation.
One other reason why manfuacturers should have their wings clipped... Whilst a major manufacturer is capable of writing SOPs such as the following, they are clearly incompetent to do so... On one aircraft, the manufacturer says that to instruct the PNF to set clean speed, the PF should say 'Bug up'. This occurs at a time when selecting the 'flaps up' will create a Staines-type event. This exact confusion has happened more than a few times, and yet continues.
Another example concerns Start Levers which have two positions, 'Idle' and 'Cutoff'. For those in training converting from piston-engined aircraft, 'Idle cut-off' means 'shut the engine down'. Really, 'Stop' and 'Run', or some other alternative. Dr Simon Bennett's book 'Human Error - by design' is a good primer on the issue.
So, operators should write their SOPs. They may wish to take limited guidance from manufacturers, but until manufacturers start to address some very basic human issues, they should not, and should not be permitted to, dictate how their aircraft are flown.