On the other hand, subsidizing high-usage customers with low-usage customers is pretty generous to the high-usage customers, and there's no pricing model that doesn't suck a little.

Pricing tiers suck if your usage needs are at the bottom of a tier, or you need exactly one premium feature but not more. A la carte pricing is always at least a bit steep, since there's no minimum charge/bulk discount (consider a gym or museum's "day pass") so they have to charge you the full one-time costs every time in case that's your only time.

Base cost + extra per usage might be the best overall, but because nobody has solved micro transactions, the usage fees have to be pretty steep too. And frankly, everyone hates being metered - it means you have to think about pricing every time you go to use something.

US cellular data plans? Where it's throttled after soft cap?

Although I will say it's been nice to have them give more transparency around their actual soft cap numbers.

You can only do it during growth phases or if there’s complimentary products with margin. The story I was told about Office 365 was the when they were using spinning disk, exchange was IOPS-bound, so they had lots of high volume, low iops storage to offer for SharePoint. Google has a similar story, although neither are really unlimited, but approaching unlimited with for large customers.

Once growth slows, churn eats much of the organic growth and you need to spend money on marketing.

Google and Youtube, especially Youtube.

Telegram?

Or they're selling their product to a market where the purchaser doesn't understand how much they would need to pay if they were paying by the gigabyte (or even how to check how much they would need). Telling those people they don't need to worry about that "detail" is a key selling point. Backblaze has a product for people who understand the limitations of their consumer product and don't find them acceptable: B2, which is priced by the gigabyte.