Some of these ULX WUs are taking 9 hours. The scoring should be proportional to the CPU time and not just a fixed number.

I fully agree.
So fast running, few credits, long running, more credits.
It is a way of calculation.

Now if some WU needs 9 hours on your monster computers, perhaps somethings is wrong !
On my very little i7-2600K; it take about 4 hours.

But I have buy a reserve of Belgian waffles to feed my hosts (only very few persons, here, can understand it)

Reuzen waffles or Luik or Brussels? LOL
I suspect you have a Reuzen Waffle cart just outside the door?
How many mice or hamsters do you have running your systems? - Maybe you get this or maybe your don't