Since you will not stop cherry picking lines from big Convo and the context, I have taken a SS of our every post during our Convo in our thread.
Please read everything and always keep the context in mind.
After that, check several key terms:
Diplomat, diplomacy, negotiation, foreign policy, EAM, Ambassador, envoy, special envoy , defense attachè, NSA and their roles.
Do a rough calculation on how many IAS/IPS officers have been posted outside, in what capacity and
why.
Then find out how many IFS officers were posted alongside them.
Compare that to number of IAS/IPS officers in India and think why isn't IFS just closed down and IAS officers assume the role mid-career. Why IFS trainee officer gets different training than his counterpart in other services.
Have some common sense and you will get to the answer why IFS officer dont become collector. And why in special cases non-IFS are given responsibility. It's nothing to do with IAS being superior, otherwise IFS, IAS, IPS will not get different training. And every IFS officer will be from IAS cadre.
Then understand the bench strength of IFS, IAS and IPS. Then you maybe will realise how MEA is rather understaffed and asking them to go serve another ministry on deputation (which they do- we only have news of high posts, not junior) will diminish the operational efficiency.