There is nothing wrong with flat-rate plans. I work at an LLM-serving startup, and am aware of at least three competitors, that (a) provide flat rate subs (b) are extremely profitable and (c) are bootstrapped, ie. not beholden to investors (there are also many other competitors but I can't ascertain their profitability or investment status).

You simply need to price the flat-rate sub at a price that's profitable when averaged out over all of your users, both light and heavy, and prevent fully automated usage by the power users. That's it. This is immensely more user-friendly, and I doubt you'd get any traction at all if you didn't do this. Even if you pay more for the sub, having unlimited (non-automated) usage frees a mental barrier to using the product. If you have to pay for every request you make, it introduces a hesitation to do anything - it makes the user hesitant to experiment, hesitant to prompt for anything of slightly less significance, anxious about the exact token consumption of every prompt, and so on. It's not enjoyable to use when you're being penny pinched for every prompt.

Anthropic's problem, of course, is that they are not bootstrapped. They don't have a business model that can compete with startups running DeepSeek or GLM on their own hardware. Non-frontier startups got to skip the whole "tens of billions of dollars in debt" step of creating a frontier model from scratch, and still get to run a model that is perhaps 80%-85% as good as Anthropic's, which is good enough for millions of customers. So Anthropic is desperate, backed into a corner, and doing anything and everything they can to try to right their sinking ship, no matter how scummy.