Thanks, Yellow Kid!
There have been several "prominant" artists I know of who used markers to ink their work - with varying degrees of success, IMHO.
The big difference for me between what Gil Kane did and Barry is partly execution - mostly, I believe it's a radically different artistic POV (or "style", as that concept is often interpreted).
Kane was almost exclusively a "linear" artist, using lines, hatching and cross-hatching to "describe form". This dovetailed with his George Bridgeman-like chisled anatomy, but all those lines, with no variation and little, if any, shadow areas of solid black often left the finished drawings "sketchy" looking or lacking substance (for me!). Compare Kane's work when being inked by Tom Palmer, Klaus Janson or Kevin Nowlan - they added in all those things that weren't part of Kane's artistic vision, and I believe, made the drawings much better!
Now, Barry - and this is just my informed opinion, of course - literally "looks" at his drawings very differently from Kane. After very roughly establishing basic composition and placement of the figures in pencil, my guess is that he uses a brush marker to do 90% of the marker rough, and maybe 10% using the fine tip marker where he has to . That methodology allows him to work with black and white shapes to design the panels instead of lines, which makes a huge difference in determining where the light and shadow areas should go - and THAT means that he's actually "painting" with the markers, rather than "drawing" with them! I believe that he's a natural painter - he just doesn't know it
I'd like to see what you did with Barry's con sketch too, if you'd care to post it!