Many robot arms use two servos for the shoulder joint. So, yes you can do that and make it stronger. Just make sure they are working together and never fight each other.

@irobot yes you can use two servos on one point of movement but the challenge is that if two servos are aligned perfect they can fight each other when they move and eventually overheat. There are ways to work Arounds. There are trim boxes futuba and hitec make to fine tune their position so they are in sync. Also RC guys who are okay with a tiny bit of wire and soldering can disconnect one of the POT sensors and jumper the servos so they share the same pot and only move together. I've also heard of eliminating one of the control boards and paralleling the output to motor connection to the motor in the second servo. Agian that ensures they will only move together. You could bench test these two methods and see what you like the best.