There's a big difference in calibre among those players, I wouldn't bundle them together by any means.

Brown, Brough - similar to Briers but not of the same quality and consistency, they best fit the "brilliant on his day" description.

McGuire, Pryce - consistent players who have been very successful in SL over a long period of time and integral in their teams winning trophies. They weren't classic halfbacks that work a team around the park but were very damaging runners.

Sheridan, Matty Smith - decent halfbacks who were not top drawer but enjoyed periods of prominence at a time when there was a lack of other talent around. In Sheridan's case, he was effective in the late 1990s but faded rapidly as the general standard in SL rose in the 2000s. Matty Smith went the other way, was seen as a bit part player moving around clubs until the declining quality of SL created a vacuum where players like him became more influential.

Richard Horne was a really good player, he was like Iestyn Harris in that he peaked relatively early. Back in around 2000 when he was only 17 or 18 he was already one of the top halfbacks in SL which was incredible. I wouldn't say he was inconsistent, but he went from being a player that threatened to be world class to a steady eddy that wasn't as much of a gamebreaker after he had had a few injuries and lost Cooke as a halfback partner. But he was still a very good player over a long time and better than players that are around today.