I cant stand Johnson really, but he's bowling better than Starc. If they have to a pick a lefty you'd think Faulkner would be the better option.
Starc bowled terribly against SOuth Africa in the second innings, which is why he got hit for 150+ runs, and sure he looked a bit better once he'd run through a tail but if the MJ era taught us anything it should be that taking wickets from trash will catch up with you eventually.
Johnson, not bowling perfectly, but making them play and causing the batsmen more trouble than Starc was (note batsmen, not tail enders).