Many aircraft are built with what seems like an inadequate amount of glue when in reality not much glue is needed in the first place. The airframe probably was fine but mechanical disadvantage on the ailerons are most likely what caused them to flutter and rip the wings apart. Some other notes to take away:
1. I never recommend the use of anything but an aluminum arm on the servo on an aircraft this size (gas or electric). The arms you have on there now, coupled with mechanical disadvantage, would eventually lead to the plastic arm failing and/or the screws pulling out from the arm extension. Use a high quality aluminum long arm like SWB 1.5" arms.
2. Putting the control linkage that close to the control surface on the control horn gives you more throw but forces the servo to have to work harder and can lead to an overly sensitive airplane. My recommendation is always to use the control horn hole that is furthest out from the airplane. This will give you the best mechanical advantage and keep the setup tight and rock solid.