Salvatore may not top Gemmel on battle scenes, no. But his martial arts background makes his hand to hand combat scenes interesting and he does well with monsters. When he came into the scene early, there was a lot of writers working on Conan style stories and this particularly is the style that the D&D people needed for their tie-in novels, so that creates a certain amount of bombast and heavy bardic language for the Drizzt tales, etc. that are tie-in. Sometimes the plotting wasn't Salvatore's but related to what they did in the games, though nowadays I would assume that's less the case. Salvatore became the favorite in that universe with readers because he does nicely with characters. The demon who causes all the trouble in his first novel, for instance, was a very fun, well-realized creature. Away from the tie-ins, Salvatore's style is a bit different. His Demon Awakens series is a more mournful, more tangled, with a monk who goes through an enormous crisis of faith and a young woman who goes through different stages of post-traumatic stress syndrome. Salvatore is also exceedingly flexible -- he can go comic and he can go dark. He is a workhorse author and he's not going to dazzle with metaphor but his ability to get readers caught up in the characters and thus their struggles has introduced a lot of people to fantasy. If you don't like his characters, then you probably are going to be bored.
Terry Brooks came into the field exceedingly rough, which even he admits. But what he did well was do a potboiler with more than most people usually threw into the pot, which made it fun because writers were just beginning to play with the form on a broad scale. He threw in epic fantasies -- Peake, Tolkein, and The Three Musketeers, and some post-apocalypse SF aspects, some comic material, etc. This was again in the Conan-favored, early era, when authors were experimenting and seeing if they could do longer stories. And again, he makes it work with characters. His young squire who wants to contribute but has been sitting on his heels, hunting on daddy's estate, then suddenly finds himself a key part in saving the world (essentially Porthos,) is an example of a character that was endearing and even complex, and it is this why people are still reading Shannara novels. Brooks greatly improved in writing style and also branched out. He does comedy very well, and his Word and Void series is quite different, a dark fantasy tale that goes both contemporary and bardic (Brooks never steers on just one track,) and is pretty well written in my view. Again, he's a workhorse author who came in when the formalized market was very new and raw and he's won a following on his characters and his little flourishes.
Raymond Feist -- who is a very good speaker by the way -- came in a little bit after the Brooks, Salvatore era, when things had spread out a good bit more for the new publishing imprints and larger books were a regular thing. Feist, like a lot of the writers at that point -- Cherryh, Lackey, Eddings, etc., was playing around with more fable structural stuff than Salvatore and Brooks' adventure tales. Though he has been heavily involved in gaming, and his books vary too, Feist was less interested in sword & sorcery and more on world building, or rather worlds building, with the 1960's, 1970's legacy of multi-dimensions that led a lot of 1980's alt world fiction to be multi-dimensional or cross-over from Earth rather than just a separate world. He tried things, sometimes very interesting things, and his characters also attracted him a following.
I think that in fantasy, it very often does come down to the characters, rather than plot, world-building or prose style. People like the characters and so they may not be that hung up on the author's use of language or even the plot, and whether they like the characters or not seems to have a lot to do with how they assess the writing, the world building and the plot.