Its funny you mention d-line pressure because i actually had that in mind when i created them. I wanted to create a set that allowed for a good amount of qb pressure on the cpu to make up for the not so good human defensive backs. However i didn't want a crazy number of sacks either. So just because you're not getting sacks every game, don't think that that is bad. Remember the average number of sacks a game a team gets is about 2.
Anyway, i would consider myself a decent madden player, nothing special. i had trouble getting pressure on the qb myself. So here are a few tips for you that i use.
1. I try not to blitz too too much. As you've noticed, the human defense back play leaves something to be desired, so i try not to leave my corners on an island.
2. Instead i'll shift my line left, right, and wide. Shifting the line out wide seems to create the best pressure for me, but be careful with that, i've been caught with my pants down when the cpu called a draw (which i loved, because that's football!)
3. If i have a speed end, sometimes i'll just move the end i'm controlling out wide an try to just run around the tackle.
4. The swim move seems to work the best for me. Like what others have said, mix it up. Sometimes, i'll just try to use the swim move and go to the outside. Sometimes i'll take the tackle outside, and then try to use the swim move to break back inside of him.
Hope that helps.