> And statistically-speaking, is viable as long as a company keeps its users to a normal distribution.

Doing a bait-and-switch on a percentage of your paying customers, no matter how small the percentage is, may be "viable" for the company, but it's a hostile experience for those users, and companies deserve to be called out for it.

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.