Coming from someone who has a daughter who is a D3 player, I think there is very little difference in individual players. I know that's gonna make some D-1 parents rage, but it's true. She has played D1 schools in Fall Ball, and also JUCO schools in fall ball, and the games have been close. The biggest difference is the pitching from these teams.
If you look at a lot of the teams in the bigger organizations locally. The lineups could be 1)D3 commit 2)D1 Mid-Major Commit 3)D1 Power 5 Commit 4)D1 Mid Major Commit) 5)Power 5 Commit 6) D3 Commit 7)JUCO commit 8)NAIA commit 9)D2 Commit etc. So why is it so hard to believe there's not that much difference in the players?

These D3 players have been facing D1 pitching for years in travel ball, it's not like something they haven't seen before.
She has played on teams where the D3 players outperformed some the D1 players in every way. Were the D1 players over-committed? maybe. Were the NAIA, D3 or JUCO players under-committed? maybe. But it sometimes is all being in the right place at the right time and sometimes it's just about fit.