I'm in the "keep him down" group right now. The Nationals aren't competing. Like every player, James Wood will slump. I'll be fine calling him up the first time he works himself out of a AAA slump. That will be real growth.
There's a confidence factor that's hard to measure and doesn't show up in stats. Jackson Merrill is just 8 months older than Jackson Holliday, but was clearly far more ready mentally in spite of less impressive AAA stats than Holliday. Same thing we've seen here with Mitchell Parker. But being "ready" for a hitter usually means a solid, .800 or so, OPS, with better things to come in season 2 or 3. The more you wait with someone who is in fact ready, the longer it will take to get to an elite level.