Also, it wasn't just about if Shuri would or would not have went to find the scientist. He came to Romonda and Shuri to find the person who made the machine or he would come back at them. He came to them because they were in charge and he knew that they would take it serious that
(1) there was other sources of Vibranium
(2) that this dude was able to get through their advanced security system undetected
(3) he claimed to have an enormous army
Even with him threatening them he still tried to come from the let's be allies perspective, because he respected their knowledge and he also on the low thought they were an easy mark without having a king around. I truly think Namor's end game wasn't really killing the scientist, it was appealing to Wakanda's fear of being bullied and consistently tested now that their king was gone.
You gotta remember, from the 1st time Namor appeared he tried to appeal to Romonda and Shuri about self preservation.... dude was trying to be slick out the gate in my opinion. Lol