You described how this is different than trap claw. Summons would not break the shield and would be rendered completely useless until one of the other units like Brand breaks it or if Annie happens to drop Tibbers on top of the shield when she summons him. As it stands, poison and burn are the only things without a counter. Glacial can be countered by qss, mages can be countered by dragon claw, low mana costs like Kindred and Ezreal can be countered with ionic spark, healing can be countered by red buff or morellonomicon, assassins and rangers can be countered by thornmail and frozen heart, high impact abilities like veigar and malphite can be countered by trap claw, and poison can be countered by absolutely nothing. If someone gets a Singed in a poison build it is basically game over unless someone's star units just outclass the poison user.