I don't think you can call Tolkien a horrible writer, especially when there are few that can write books as good as his and as memorable as Lord of the Rings or the Hobbit.
Good literature is often forgotten, but good stories last for an eternity. Proof of this is, most the stories that last over the centuries that people still read today are good stories, and you have to remember stories are a form of literature.
You say it's bad art, but im asking how, being able to paint a fully complete vivid picture (not a picture with different pieces missing) in your mind, and also being able to understand the races surrounding the character. You have to remember that is needed for fantasy and is the reason the fantasy genre took off, there would be no fantasy genre without Tolkien, and that is for a reason. If Tolkien's books were bad art than you wouldn't see his books spawning an entire genre of art.
Tolkien did not like writing allegories and such and was detailed on everything, yes, and somehow he was able to fit all that detail and the whole epic itself within his 300 or so pages. You can see the environment the characters are in completely in your head, some people hate that yes, but I personally love it, it allows the entire book to play out better, and the story to catch on more.
You also must remember why, and how Tolkien chose to write his book, what was he writing it for. When it came to the Hobbit, he was doing multiple things,
1.Creating a mythology, that is what he wanted to do, he was writing an epic not a short symbolic novel to make you think real hard
2.With Bilbo it was almost symbolic of Tolkien's own experience in World War 1, Tolkien was dragged in, not wanting to fight (go on the adventure) and preferred his simpler life much more. Now im not sure if this was on purpose, but it does indeed connect, Tolkien wrote Bilbo's story symbolically maybe intentionally maybe un-intentionally we don't know. Only thing we do know is that the races in Lotr don't represent European nations that was the one set of allegories I remember him saying were not true.
Also remember everything Tolkien wrote in his books was very much his own when it came to the creativity and thought process, sure every fantasy out there now has elves and dwarves, but they came from Tolkien's books.
But then in the end he still only wrote a story, and wasn't trying to write a 'literature piece', which I find stupid as a point of why he barely received any awards for his works, since 'literature pieces' originated from stories and are in fact stories. Most people when they pick up a book it is for a good story, and if it has other symbolic meanings and such then great. Few people however pick up books so they can critically analyze it and grasp at a million straws to find its 'deep meaning'.
Honestly literature would be a much better if it had more good stories, and less writers trying to be 'artistic' when great stories are artistic just from being a great story. Because honestly most the writers trying to be 'artistic' all use the same general themes, and write the same general story, there isn't any creativity in it.
I enjoy the writers trying to 'artistic' when they write poems because poems aren't meant to tell a story, they are meant to convey a message. A story is meant to convey a story and its themes present a message through the story, a story was not meant to be critically nitpicked a part to follow the delusion that every specific word in the 200 page novel has a very specific meaning like it would in poetry. It's there people start grasping at strings for things and the delusion stories are deeper than they really are. (Yes some are deep, but when you get to the point where you have a person saying, 'omg at the end of the story the guy said "Come on George lets go have a drink" it must represent communion! SO DEEP' Its annoying, and that type of over thinking shouldn't be awarded.