I have some issues with the above statements as I think they are somewhat of a generalisation or an over simplification unless I have completely misunderstood the PND 90.
Having looked through the PND90, I for one,have no idea where I might put potential remittances, like pensions for example?
In past interactions with Revenue Department staff in Jomtien for claiming simple refund of withheld interest the helpfulness was mixed at best. Not being fluent in Thai and even with a "helper" I could not imagine trying to complete this form with them at this moment.
Perhaps it is just me (probably ) but as someone who has completed UK paper forms for some years now with the help of the Notes I can't see the Thai return being a "simple affair for most people".