out of curiosity, is it not possible, feasible or practiced to have a fast aircraft behind, descend thru my level and speed past me while i fly slowly or on divergent heading?
Of course it is- please give more credit than that! But if the 320 pitches up at the FIR boundary 10 nm ahead of the 777, and we do nothing, they will arrive final app (or whatever point they need to be apart from each other) at the same time. Option 1 is to reduce the 777 and speed up the 320 (this is probably the most efficient and least work for the controller). Option 2 is to slow the 320 even further, and probably vector as well (because the 777 will have to catch up the 10nm it is behind AND get another 10nm ahead). How this is efficient for the 320, I don't know. So, the continuing on at .74 is a FALSE economy.
Not only that, ALL THE OTHER inbounds have to be worked in- you are rarely looking at just a "pair".
What would actually be efficient is if we had an over-arching "MEcontrol", such as Eurocontrol. At the very least, someone looking at whether Doha was going to hold them, thereby negating any sequencing being done by Bahrain, UAE etc. Let them steam on into the hold at whatever speed they wanted, just setting up holding instead of in-trail.