Великий does not mean "very good". It is about "greatness" in the meaning of being important, influential, prominent, innovative and leaving a great legacy.
For example, you can say that Shakespeare was a «великий» playwright because he was THE one most important playwright of the time, shaping what was after and still known today due to his influence on writing. You cannot say the same about the great film you saw yesterday, unless you are 100 % sure this film is historic, showing things to be understood and learnt from by all filmmamers of today. Typically, this can only be said in retrospect.
That make sense, thank you. But, and I might just be slow today, I still don't understand the difference between Прекрасный and великий.
You said "Прекрасный would be understood as "great person""
Maybe it was memrise, but I could have sworn there was a question in this course that translated "great person" to "великий человек".
Originally, the word красный meant "beautiful"
The way the meaning transformed is easy to follow: "beautiful" becomes "striking, bright", then "vivid, having a bright colour", then just "red". It didn't have to go that way but it did. Nowadays the "beautiful" meaning can only be found in set expressions and aphorisms.