Are Australia's fast-bowling reserves really an Ashes problem?

Season 18, Episode 30: Another couple of next-gen fast bowlers have gone down injured in the last week, with Spencer Johnson again withdrawn from duty and Lance Morris out for a least a year with major surgery. Is there an emerging problem for Australian quicks behind Cummins, Starc, Hazlewood, and Boland, or does their presence mean there is no problem? Also this week, Mitch Marsh's team rack up 400 after losing an