It is quite obvious that there is a huge rift between developed and developing countries in the world in terms of economy, education, defence, etc. Similarly, there is a distinct barrier between native English teachers (NESTs) and non-native English teachers (NNESTs). Without a Cambridge DELTA or TESOL certificate, one can hardly study ,migrate or teach in an English speaking country.
As English is the international language of communication, the pride of native English teachers significantly grows with more need and demand across the globe. To be honest, Cambridge English language learning and teaching courses are applied in abundance to ascertain the teaching credibility. But the sad truth is that, though many people possess a PHD in English with national teaching certificates in their own country, they are not eligible to teach internationally as they happen to be non-native teachers. Even if one obtains a degree and CELTA, TESOL or other recognised teaching qualification, an international job is not assured. Perhaps an MA degree in Cambridge may help to procure a better job. There is nothing wrong in taking International teaching and training accreditations, but with the void in national accreditations, it becomes improbable. Every day of one's continuous professional development becomes irrelevant and meaningless.
Personally, I would suggest that there is no difference between NEST and NNEST teachers, as teaching any language is just the desire for updating and promoting the teaching and learning skills in that language. For instance, a native English teacher may be not good at teaching grammar whereas a non-native teacher may excel in teaching this. Moreover, English medium schools, colleges and universities are widespread worldwide and English language teachers are doing great jobs even without a CELTA or TESOL qualification.
Teachers who possess an inherent quality with passion and desire towards teaching grow their skills and update in their continuing professional development. All teachers do not cherish this attitude to grow professionally. I would conclude by stating that there is little use if there ever exists a disparity between the NEST and NNEST in future.