your guess is on the spot - ability to consistently win points out of short return is one of the things that separates a low 4(like me) from higher levels I imagine. I usually win against guys who tend to hit deep (even with pace) - it's been difficult to adjust or stay motivated to tackle slow shots or slow serves ( "he can't hit a proper ground stroke - do I really bother..." thinking ) until I'm a break or two down and uphill battle from there. Definitely I'll take such players seriously next time from get go (in addition to treating the short balls properly which is an easier thing if you expect such a strategy) !
It's way easier to play against opponents (like mid 4.0 players) who have grooved "proper" groundstrokes, but not sooo grooved that they can hit away from you consistently, because they typically want to hit hard, but don't have quite the control to hit away from you, so the balls tend to land short, and bounce right up to where you're standing (center hash mark), and usually in your strikezone not requiring you to move too much.
I've played 3.5 to low 4.0's that I swear hit just as hard as I do when I'm bashing the ball to them at the center hash mark (or they might take 2-3 steps back if I happen to be hitting deep),... and they'll even T off and hit winners (when we're supposed to be hitting "cooperatively")... but as soon as a "real game" starts (or groundstroke games - since usually their serves are terrible), I can literally just throw up lobs and win because they can't move and hit... then they wonder why they were hitting so well in practice, but found the back fence when playing "for real".
Playing players with poor erratic technique (or short choppy "pushers"), are a nightmare because they hit all over the place (intentionally or not)... they don't hit hard, but since you don't practice moving AND hitting, you lose due to unforced errors.
Main thing for you to practice in general would be to move and hit. So after the warmup,
* don't let balls bounce twice,...
* even if a ball is just out, reach it, and hit it anyway.
* keep moving, split stepping, etc... in between strokes
Presuming your fundamental strokes are decent.... If you're out of shape, you're better off practicing for 30 min of "run every ball down and try to hit it back with good technique", than spending 3hrs hitting easy fed balls from the center hash mark (though admittedly this is often therapeutic to me!)