This is very true - the basic Boeing or Airbus spec is an empty box.

All the seat manufacturers seem to be either in North America or Western Europe, and they all serve a range of airlines from across the world. So whether the airline is from a developed country, or one less so, is not an issue when it comes to seat comfort. Meanwhile the leasing company that owns the aircraft will want normal international standards, so if they have to take the aircraft back they are not restricted for who it can be remarketed to.

The same international approach is true of the overall F or J experience, which for smaller nations' carriers will probably have been designed and specified in fine detail by consultants working out of London or LA, for example.

I would say that the tightest pitches are generally not found in third-world airlines, who do not usually take minimising seat-mile costs to the extreme like some European/US ones do.

Aviation has done a bizarre thing, for as the general population has got taller/bigger as the generations pass, seat pitch has gone the other way!

Actually altering the seat pitch in a modern aircraft is quite an expensive engineering operation. Moving the seats is just the start. All the overhead services for lights, supplementary oxygen, etc have to be reorganised, as do the IFE systems, galleys have to be rearranged, etc.