Trustmark's dimensions down the Right field lines and dead center are actually deeper than Turner's. I'm not sure how the power alley's compare, but Trustmark is not necessarily known as a launching pad. Talking to people who actually have played there, if you hit one out of the yard at Trustmark, you earned it, no matter what level you play at.
Trustmark:
Left: 330'
Center: 402'
Right: 332'
Turner:
Left: 335'
Center: 401'
Right: 330'
Also, Turner is known as one of the lowest ranking parks every year in terms of home runs (mainly because their clubs center around pitching) and run production. It is very much known as a pitchers park, so it makes sense to have Pearl reflect that.