There’s definitely benefits of learning a specific structure and I think you should practise using one. I like PEAL because it’s very simple. The most important part is having a coherent and clear line of argument, so make sure you have consistency throughout with your LOA & don’t leave out the conclusion!
As for vocabulary, don’t get hung up on sounding fancy or smart, as they want to see effective communication skills, which could be hindered by complex word choice.
I’d recommend reading articles on different topics (Science, food, law, politics etc.) and spacing out studying - you’re not memorising anything you’re trying to strengthen your skills.