It's probably that the Humbrol had too much matting agent in the varnish - I used to use it, but stopped for exactly that reason. For the way I prefer to work, I've found that a quick squirt of Dull Cote over the dry Quick Shade, followed by 20 minutes in the oven at 60°C, gives the most consistent finish.
I tried the Vallejo, but found that, for my particular tastes, it was a little glossier than I like... But that might have been the way I was using it...
One man's meat is another man's poison and all that!