Where would his quality rank and the pantheon of English/Scottish 'smiths?
It is not wise to try to generalize an individual gun's quality based on the maker's name. The wiser approach is to learn the Brand Value level of the maker's name and judge the quality of the gun in question independently of who made it.
So, to kick off the above, Dickson has Brand Value level two (BV2); so sayeth the market. When you are looking at older guns, you may fairly safely assume that 75% coverage of fine or deep engraving, high grade wood, fine checkering, and tight joinery equal a best work gun. All makers were capable of getting out a best work gun or a farmer gun. The price of the gun determined what quality you got. With Brit guns, you are very unlikely to find a "tart" (a low quality gun with lots of embellishment).
DDA