I don’t assume this at all. In fact, the opposite has been happening in my experience: I try multiple providers at the same time and the $20/month plans have only been getting better with the model improvements and changes. The current ChatGPT $20/month plan goes a very long way even when I set it to “Extra High” whereas just 6 months ago I felt like the $20/month plans from major providers were an exercise in bouncing off rate limits for anything non-trivial.
Inference costs are only going to go down from here and models will only improve. I’ve been reading these warnings about the coming demise of AI plans for 1-2 years now, but the opposite keeps happening.