Not really. Suppose giant A undercuts startup B where A is making a temporary loss but B runs out of money trying to complete, only A remains in the market and A starts charging a premium since it doesn’t have completion.

This is bad for customers in the long term. Like how Amazon is slowly destroying brick and mortar stores, or having Amazon Basics at the front undercutting other sellers. Monopolies mean you don’t have an open fair market anymore.

It's possible that there could be non-obvious innovations in how to save money with a low reliability threshold, which Amazon might not be able to effortlessly copy.

You are confusing "cheapest option possible" with "cheapest option available". Maybe Amazon _could_ be cheapest and most efficient in everything but they aren't, that's why they make a lot of profit with their cloud services. Thus there can easily be a competitor with a cheaper offering, especially if they are cutting some corners as per the article, even if they have some inefficiencies in other areas.

... better than AWS with its SLAs, that every major company relies on to some extent?

Quantity is a type of quality. Lots of people mainly use cloud storage as a cold storage locker for backing up photos and documents. I'm sure there's ways to innovate in the space that would make certain clouds more appealing, but most solutions are already effective as simple storage lockers. Doing it better instead of cheaper at this point is more likely to be either a megacorp affiliation perk, like a discount on a YouTube Music subscription, or phone company style family plan discounts "Get discounted storage for the whole family if you pay slightly less than the price of four memberships!"