The reason why someone would be bad at RCs is because he/she does not do it via 'structures'.
Building your verbal skills require a lot of work, and it needs to be done step by step.
You should start by understanding what the part of sentences are i.e if you see a sentence what does each part does ( is it a noun, a modifier, an adjective, it is an essential clause, non essential clause etc)
What happens in an RC is only retain a part of the information that you read. So you should read only the part that is necessary in your first read. 'Reading everything' would only lead you to retain bits and pieces of random information.
There are lot of ways you can improve on an RC or verbal for that matter, but it would not be possible for me to outline everything on one post.
However, I strongly believe that anyone can get a 35+ on GMAT verbal. You just need to have a proper approach.
Hope this helps
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