The supply of military aircraft should be entrusted to people who have prior military experience in producing same, and how critical the into service date can be.
Ah, the old,
"you can only go if you've been before" mentality!!
Even if we do as you say and stick to "existing" suppliers, there are no viable alternatives at present.
"Fatter" Albert will be 2020 at the earliest provided it even gets off the drawing board,
C27 is too small all together,
C130J is too narrow,
C17 is too big for intra-theatre tac work (great for strat and for US style "Tac" work).
Antonov in any guise is not politically acceptable, nor technologically able.
Face facts, A400 might be delayed, but it is still the only realistic option in the current environment.