You're comparing a product from one of the largest companies on earth with an upstart. and even the cheapest ad-supported Kindle is only 2/3 the price of this in US?
The cheapest Kindle is routinely on sale for $60-70. And spec wise there is really no comparison. The Kindle has a backlight. 1448x1072 resolution (compared to this one's 800x480). Battery that can last a month. USB-C. 16GB storage. Bluetooth. It's a very capable device. The fact that this one is made by an "upstart" means nothing. You have to compete on price and quality to be successful. Plus if this company goes out of business and shuts their servers you are left with a $150 paperweight.
Anyway yes the Kindle has better spec but as you mentionned in your first post the fact that it's locked is the whole point. Amazon is not making money on the device ...
Keepa doesn’t always tell the whole story as it can’t track coupons and in-cart discounts, which Amazon regularly uses especially for their own products to hide the real lowest price from price trackers and scrapers.
The largest company you mentioned outsourced the manufacture to factories like Foxconn. A common pattern of those "upstart" is they are just a different thin wrapper around some other factories, with a crappier spec but able to sell the BOM with higher prices.