I don't see how this would explain a disincentive to charge higher prices.
EDIT: ofc in the Twitter thread, there's few disputing that if this is actually true, or if maybe Apple does different things in different markets, etc. so everything with a grain of salt I suppose
Take other payment processing platforms like Stripe as an example. Stripe charges $0.30 + 2.9% to process a purchase.
To help build your (and my) mental model: Price of item -> Stripe revenue (rounded)
$1 -> $0.33
$5 -> $0.45
$100 -> $3.20
Apple's 30% cut makes sense if they were expecting most apps to be roughly $0.99 (anecdotally, I remember this being true during the early days of the App Store) and the (presumed) few apps that cost more than $1 would be the "whale" developers that would subsidize Apple software development. But nowadays apps are a lot more powerful, feature-full, and development-intensive so higher prices are required for any hope of profit.
So the math you have is right, it's just that the path to profit is a lot harder when the ONLY way to sell your product is to have >=30% cut out immediately upon sale. Some stores set a minimum (e.g. $5) sale amount for using a credit card and those payment processing platforms have fees orders of magnitude less than Apple's App store
(Sales not refunded * 0.7-refunds * 0.3) * price
If
Sales not refunded/refunds<0.3/0.7 ~ 43%
Then profit can be negative (you lose money because more people refund than not).
>57% refund rate literally makes you lose money from listing. But even if just quarter of people refund that eats almost half of profit.