The main point is that we probably don't need Hall any more if Harper can play 1B. And secondarily putting a decent defensive OF in the lineup that gets Schwarber out of the OF (and really we need to focus on Schwarber because Castellanos has actually been average defensively of late) is just more valuable than putting Hall in at 1B where the defensive improvement is minimal before we even get to the bats.
We all know Clemens is just keeping a roster spot warm. It is nice that it looks like we have some good defensive OFs that we can play that are now offering a little offense. Pache can replace Guthrie. Who replaces Clemens eventually (Hall or Cave or Muzziotti) is a little bit more interesting.
And in terms of other OF options, check out Jhailyn Ortiz' BB/K rate. 54 plate appearances. 46 AB, 6 BB, only 9 Ks.