A garage door should be counter-balanced with springs to a point that you could raise and lower it with one finger. This also includes proper alignment, lubrication and other adjustments.
If the door is properly adjusted and lubricated, the door opener has very little work to do.
Since your opener pulled loose from the door, it must have a pretty powerful motor. I would check for springs on each side of the door that are around the cable that lifts the door; OR the springs may be in the middle of the door, coiled around a shaft which winds up the cable on each side. These springs can be replaced in either case. PLEASE USE CAUTION when working with the springs, they can break an arm or make a tool slap you up the side of your head. The springs must be held in control at all times; the center shaft springs can be held with vice-grips or pipe wrenches, while the side springs can be held by threading a cable through them and tying them tightly.
Let us know how you work it out.