How can they bring back Lich King only to destroy him!?

I have not played WoW in years. In my opinion after Lich King the game has sucked. So you can imagine how happy I was to see he was finally back in this new expansion. Then as I watch the cinematic he is easily defeated at the Frozen throne no less!! Wtf…how and why? How can they destroy the best character in all of WoW and by someone he has easily defeated in the past. Is it that Arthas was more powerful, or was it due to Frostmourne? Very disappointing.

The Banshee Queen was more powerful and Bolvar isn’t gone or dead, she took his crown and opened a rift. And if you take note, she never had these powers in the past, because of the Jailer she has become stronger.