Of course you don't NEED the better models, but figuring out what model you need can waste a lot of time and effort. Even when a cheap model is capable of a task it needs a lot more guidance than a more expensive one. They are also less reliable. You can waste a lot of time cleaning up after them. Judging whether something is good enough is hard work and rerolling with a more expensive model is painful. Judging the difficulty of a task ahead of time is very hard. Judging how good a model is for a given task even harder, especially when models and harnesses keep changing all the time. The real productivity boost LLMs provide is already modest and when you start tinkering with models it can easily evaporate.