Hi!
I used to struggle with the same thing, and what helped me was starting with more detail before stripping it down. Instead of going straight in with bullet points, I'd first write out a brief plan of what I wanted to say - almost like a mini-script or structured notes. Once I was happy with the overall structure and content, I'd then reduce that into succinct bullet points of the main topics (e.g. "Intellectual Challenge", "Practice Area Expertise", etc.)
From there, I'd practice it: first using the full plan, then using only the bullet points, and eventually just trying to recall the general structure from memory. By the time you then record the actual answer, it's easier to remember the depth of the content without having to read from a full script. I still found it useful to have the bullet points on a post-it note in my eye-line, just so I could refer to it if my mind went blank! This approach allows you to go into more depth on your points, as it helps you remember the depth of what you want to say whilst also giving you room to add ideas as you go along!
That being said, the above approach is mostly applicable to VIs with unlimited preparation time (unless you can write a super speedy plan and practice!). If you have limited preparation time, I would try to focus on 2-3 key points and go into more depth - for example, include previous experiences and discuss how they created an interest in a certain area or motivated you to apply for this specific firm. It's usually stronger to go with quality over quantity, particularly if you are worried about your points sounding vague
I hope that assists
