My long draw is totally unpredictable in both rebound speed and direction.
In most cases, the miss direction can be traced to an off-center hit on the object ball but speed of the return is another matter entirely.
To be effective, a draw must bring the cue ball back to a specific point without swerving left or right.
On long draw shots I don't think swerve going to the object ball plays a part. The cue ball is sliding all the way to the object ball so it is traveling straight. Hitting the cue ball off center and not aligning to the shot properly are the reason why you have trouble drawing back straight.
On draw shots with sidespin, after you make contact with the object ball, the path the cue ball takes can be altered quite a bit. In practice sessions, try cut shots with slight angles and low inside and outside English. There are positional shots that can be made that many players have no concept about. I am talking about the path the cue ball takes right after striking the object ball, not after it hits the OB and then the rail and the english takes effect. You can minimize angles and create big angles with this. You can even draw straight back on slight angle cut shots.
But you will find the draw shot difficult to position accurately. If you have the option utilize a follow shot, it can be hit more gently and with more control.
With the final shot, go for as much follow distance as possible.
If you get a chance to watch them in action, I think you'll find that most, if not all pros prefer to go forward with a follow shot rather than trying to draw the cue ball back. The reason is that draw is the most difficult english to control. Not because of any swerve that is imparted to the cue, but because the speed control can be radically different between two tables, even if the equipment and carpet are exactly the same. Follow is MUCH more forgiving of deviations in shot strength and spin.