That's a fairly long tail (by modern t20 standards) and Amla really? Belongs in the test imo. Also a liability in the field. Morgan is good but not good enough for this team if I'm honest, and Afridi is very hit and miss! Would rather have Shakib (offers more with the bat than Afridi) and Dhoni (always dependable in the shorter formats).
Afridi, Anderson and Johnson at seven eight and nine is hardly a long tail in a twenty over game!!!
As regards Amla, yes really. Its all well and good to pack a side with hitters but what happens if the pitch is a bad one or three are blown away for little or nothing? You need at least one proper batsman in the side and Amla is the best bet at that role for me - he is classical, but hits the ball hard and in good areas. If the boom boom boys come off, he can always step aside gracefully, but if not you'll be glad of having him there.
Morgan is a similar thought process - he is a bit different from Gayle, Finch, ABDV and McCullum and asks different questions of the bowlers. He's ever bit good enough!
As for Afridi vs Shakib....really? Afridi with the ball is quality, and complements the rest of the spin attack well for the type of pitches likely to be seen, whereas Shakib is easier to get after and, if a little more reliable with the bat, less explosive which, for a guy batting seven, is not ideal.