FYI it’s “dramatically improved” not “drastically improved”. Drastically has the connotation of something bad happening so it doesn’t make sense to drastically improve something, it’s like saying “horribly benefited”.
Not really, as people in some dialects do so horribly/terribly improved. Drastic doesn't even mean bad per se, it just means extreme.
The connotation of drastic always being negative is through common usage and not strict definition. See: https://www.merriam-webster.com/dictionary/drastically
Using drastic in this instance is an appropriate, but rare, usage in a positive sense. You are correct that dramatic would be a more commonly used neutral synonym, but using drastic is technically just fine here. It is only slightly odd usage by common practice, but as a native english speaker I hardly noticed it until you pointed it out.
By using a less common word and outside of the common usage of that word, to my ear this adds emphasis, like reading the word in BOLD text or capitalized.