I agree, it's amazing that Warsaw (as well as Berlin, London, and Tokyo) were all able to bounce back from the destruction they suffered in World War II to become large international cities that they are today.
Tokyo's fate was tragic, too, as was of Minsk, the capital of Belarus. Those are perhaps the only world capitals that compare to Warsaw in terms of the proportion of material losses in WW2.
But neither Berlin's, nor - much less - London's destruction, cannot be put on a par to Warsaw.
And...
Let's not forget the human toll. In 1939, Warsaw had ca 1,3 million inhabitants.
More than 600,000 of them (ca 50%) were murdered by the Germans throughout the war. That number matches all British and US casualties of WW2 combined! London itself lost some 15,000 inhabitants. As for Berlin, some 50,000 Berliners lost their lives as result of air raids, and street fighting by the end of the war.
Considering Berlin's pre-war population of ca 3,500,000, the proportion of its human casualties did not exceed
2%. The destruction of urban fabric is estimated at
50% (mainly concentrated in strict city centre).
Once again:
Berlin ca
50% destroyed ---
50,000 inhabitants dead
(ca 2%).
Warsaw ca
85% destroyed ---
more than 600,000 inhabitants dead
(ca 50%).
Also, it must be said that Berlin never ceased existing nor functioning as an urban/social entity. While Warsaw between October 1944 and January 1945 was not only nearly completely destroyed, it was also totally deserted, as surviving inhabitants had been deported by the Germans to forced labour and concentrations camps (some were delivered to other areas of Poland to their own fate).
Finally, to this it should be said - Berlin was capital of the aggressor country. Warsaw was capital of the victimised country.
Thus, there was a time there was actually no Warsaw anymore, to put it straight. That probably did not happen to any other world capital in the modern era.
And so said gen. Dwight D. Eisenhower, who visited Warsaw in September 1945. Shocked at what he saw, he declared having never seen a big city as terribly destroyed, as Warsaw.
Having said all the above, the rebuilding of Warsaw cannot be compared to reconstruction of other European capitals,
because it entailed the rebirth of a dead city.