I think the people who want Austin Jackson basically just don't think Saunders will be healthy enough to contribute at all. Bautista also comes with age based injury concerns.
Bautista --> old; injury risk
Pillar --> the offensive downside is real
Saunders --> massive injury risk
Pompey --> prospect risk
It's not difficult to understand the desire for one more viable OF.
Good roster construction involves creating robust rosters that do not crack when faced with adversity.
Great roster construction involves creating anti-fragile rosters that can potentially respond positively to adversity. Part of that, sometimes, involves putting talented prospects with options in AAA.