Yes he should definitely be in the outfield. But there could be a period of time when the doctors say the throws at 1B are better for him than the throws from either OF spot. Plus, there is a need with Hoskins and Hall out. If Hall comes back that need may mostly disappear.
Options are never a bad thing too. Limiting Bryce to DH (which will happen the first month or two regardless) limits the team to some degree. They can't DH Bohm for instance. They can't DH Schwarber and Castellanos. They can't DH JT. I want the option to do all of that. If the only position Bryce can play is 1B for a month or two then that helps the team even if he does it only occasionally. And there is no reason he can't do it with a little practice and his innate athleticism.
As for the future, we definitely want him in the OF. That was the whole premise around getting Schwarber and Castellanos to alternate at DH and that logic has not changed. But we don't have a 1B. Bohm is a better player if he can play 3B in the lineup than 1B. We still don't really know if Hall can hit well enough to even do the long side of a platoon job (though he'll get every chance if healthy).
I don't think Bryce ends up playing more than 10-20 games at 1B this year, but if he does it probably will help the team. And he is such a baseball lifer and student of the game that I have zero doubt that he will be adequate at the least important position defensively.