See even Draupadhi's vastra-haran wasn't stopped by Shree Krishna until the final moment...lot of things were done to her and pandava's before that which was were equally cruel.
Draupadhi's vastra-haran became the foundation of mahabharata battle...because with out it Pandava's would not have attacked Kaurava's to stake their claim.
As for Abhimanyu i wouldn't say it was done to bring pandava's out of their comfort zones , because they had already killed their most beloved grand-father before it and bhim had killed 50+ kauravas by then.
So, they weren't lacking in conviction of war , but yes it became foundation of killing Dronacharya and Karna when they were weaponless.
Abhimanyu's brutal, cruel, in-human killing symbolizes what Kaurava's stood for and how brave Abhimanyu was!
Draupadhi's children getting killed lead to punishment of Ashwattama for betraying his father and being co-culprit in every heinous act of Duryodhana