This article talks about pre-draft scouting reports on Moniak.
A very vocal booster, pre- and post-draft, was Pat Gillick, who described Moniak as having among the very best contact swings he had ever seen in a draft candidate. It was a level swing, which stayed in the strike-zone a long time, according to Gillick.
Moniak was expected to hit for average, with a ton of doubles.
The Phillies development staff tried mightily to increase his HR production. Very possible this ruined him.
I never saw a scouting report which described the pre-draft Moniak as a slap-hitter. That's how Quinn was described.