The ending of Thor: Ragnarok destroys Asgard on purpose, and Thor accepts the loss because Asgard was always its people rather than its buildings. Thor decides that the only way to stop Hela is to let Ragnarok happen, and Loki places Surtur's crown in the Eternal Flame. Surtur is reborn and ends both Hela and the realm. The survivors escape on the ship, Thor takes the throne, and he and Loki make peace.
What was the point of Thor: Ragnarok? In my opinion, the point is to finish Thor's arc from heir to king by taking away the kingdom. In Thor (2011) he is a proud prince about to be crowned, and here he wins the crown only when there is nothing left to rule except a ship of refugees. It could be argued that this was the most radical thing a Marvel film had done to one of its heroes at that point, since it also costs him his hammer, his eye and his home.
The ending also sets up what follows. The mid credits scene shows the ship stopped by a huge spacecraft, and later films link that to Thanos. In Avengers: Infinity War, Thanos's forces attack a ship carrying Thor and the survivors of Asgard, and Heimdall sends the Hulk to Earth to warn the others.
Is Ragnarok the best Thor movie? That is a matter of taste but, my pick is yes. It has the strongest ensemble of the four Thor films, a villain in Hela who wants the whole kingdom, and the best use of the Hulk outside the team films. It is also the highest earning Thor film, which at least shows that audiences agreed in large numbers.