The usage limit on your $20/month subscription is not $20 of API tokens (if it was, why subscribe?). Its much much higher, and you can hit the equivalent of $20 of API usage in a few days.
Their bet is that most people will not fill up 100% of their weekly usage for 4 consecutive weeks of their monthly plan, because they are humans and the limits impede long running tasks during working hours.
I do believe it's unreasonable. The limits are the limits, you reach them there's no more free lunch after.
Fix the limits, so the limits are reached at a rate that sustains their business.. ? obviously this WILL happen eventually when they need to pay for things.
"A rate that sustains their business" at the moment probably looks like API pricing or maybe even higher. That means subscriptions get significantly more expensive and/or limited, which is maybe where things are headed.
API limits are infinite but you'd blow through $20 of usage in a maybe 1 hours or less of intense Opus use.
The subscription at $20/mo (or $200) allows for vastly more queries than $20 would buy you via API but you are constrained by hourly/weekly limits.
The $20/mo sub user will take a lot longer to complete a high token count task (due to start/stop) BUT they will cap their costs.