Not true. I weigh only 100 pounds & have a chronic illness. I always install my seats without help.
It's about leverage -- just 1 arms' worth of pressure onto the seat while the other arm tugs should be adequate -- it usually helps me to pull toward the opposite side the carseat rather than up or out.... The Apex in particular often merely appears to wiggle around too much because it has thin "feet" under its base instead of the sturdier bottoms of most seats (this is probably related to the requirement of a high vehicle seat back, too).