I keep going back to the BET comic for Black Panther from 2010. But they actually got this right. They showed Shuri as able to fight in training so it would make sense for her to be able to take up the mantle.
And all they had to do was toss in a throwaway scene of her in a gym sparing to show that she can fight but nope didn't do it.
And yeah Coogler etc..made the terrible decision to make T'Challa of average intelligence in Black Panther while Shuri was the genius. Which made no sense.
Because he was supposed to be a combination of Tony Stark, Mansa Musa, Bruce Banner, Reed Richards, and Batman and Coogler decided to make him just an average leader and average fighter who got beat by some random dude from Oakland.
Maybe he just didn't like the character or couldn't "relate" to a high achieving Black man. Who knows.