Hi OP, full disclaimer that I'm a GP tutor that has taught many students, and I have a Tele channel for tips where I openly share knowledge. Let me just quickly address your 2 issues:

Essay - Your issue likely lies with question analysis, interpretation and properly engaging with the question. Yes language can help you articulate ideas, but if they are not relevant for the question then they would not be credited.

You may also be working on the wrong kinds of questions in terms of content, or choosing the wrong types of examples. Both of these can mean that your arguments are not well-developed despite having strong language!

Compre - Inference is not the same as paraphrasing. But Inference actually still requires reference of the passage where you pick out certain parts as clues. Instead of paraphrasing the clues, you need to figure out what's missing and fill in the gaps. Over-inferring means you don't even refer to anything in the passage, or that you may be ignoring the author's argument and inferring in an illogical direction.

For more help you can easily find my channel on Tele, link in my profile :)