Arduino IDE shines when you're building something small and simple, where the code is at most two pages long. That satisfies a majority of the original use cases for arduino. e.g., my first use of it at work was to toggle a relay on and off once per minute to catch a problem with a new design that only happened at power-on. That was probably under 10 LoC.

However, in the intervening 15-20 years, people have been using arduino for increasingly complex applications and the basic IDE really sucks for that.