What explanation was given for Tony Stark's superscience? How about Bruce Banner's? Hank Pym's? The only explanation is they are all geniuses and therefor any technology they want to give those characters is to be accepted. I'm not sure how that's different with Shuri.
Also, what specifically is over the top about Shuri, as opposed to the other such characters Marvel has used in the movies?
Correct. Tony Stark's super science requires a suspension of disbelief. You need an additional suspension of disbelief, that the answer to so many problems, ie build an army of Iron Men, is never done.
Bruce Banner's super science requires some suspension of disbelief, though his super science is not that super, and it is very believable that they don't want to do that to more people.
Hank Pym's super science requires suspension of disbelief. His accomplishments, seem less world saving than Starks, so the lack of an army of Ant Men, seems more believable.
Shuri's super science requires a suspension of disbelief. THat she is super science, at age 16 as opposed to the other Mad Scientists listed, who mastered their fields as adults, requires another suspension of disbelief. That her brother is a super hero, requires another suspension of disbelief. That her family maintained secrecy of hiding a secret the size of a nation, for centuries, requires another suspension of disbelief. Vibranium, requires another suspension of disbelief. That a nation ruled by a warrior king with a warrior culture, and a massive tech advantage, never waged war, for centuries, requires another suspension of disbelief. The cloaking field, requires another suspension of disbelief.
Seven is a lot more than one or two. That is what is over the top about Black Panther.