Lots of places all over Europe were a lot more heavily bombed than Hull and had thousands more casualties. They don't use it as an excuse for ever failure in the city 70 years on.
The most bombed area in the war was Malta.
I was talking to the bloke who runs the charity raising for The Hull People's Memorial, and he told me about how Malta received the George's Cross for it's war efforts. The Maltese president visited Hull to view the bomb damage and he said that Hull deserved the George's Cross much more than Malta does.
I think you can and can't blame the World Wars for Hull's fortunes since. It's more a case of the city being in-directly suffering since the war, because of it.
Not only did Hull pass up on gaining funding to re-build after rejecting Abercrombie's masterplan for Hull, but I think the Government saw it as a lost cause due to the damage. A lot of Hull was rebuilt by the people of Hull itself. Local businessmen saw it rebuilt, for example the CECIL cinema on the cross-roads opposite Anlaby Rd was the first built post-war cinema in the UK. I imagine the government was happy to let Hull rot, and didn't expect the fishing industry to appear and keep it alive.
You can see that ever since WWII, successive governments have been determined to create 'cluster' 'city regions' for people to live/work in. You only have to look at the billions pumped into post-war Leeds, compared to post-war Hull to see this - Hull was heavily bombed, Leeds was barely touched... Leeds has probably had 10 times the amount of funding that Hull has since WWII.
We had a boom during the Victorian/Edwardian era which saw a lot of grand buildings made, unfortunately the next 'boom' was during the 50s/60s which saw a lot of buildings appear, which are still around today and look dated... it seems Hull's next 'boom' is overdue, but I don't doubt it's time will come again, as it has throughout history.