What do you mean by install?

Arduino's IDE is nice for some boards since you install the software and everything is ready to use, but that is only the case for some boards.

PlatformIO is mildly more difficult to install since it is a two step process: first the VSCode, then the extension. Both steps are easy enough to do and to some people it is preferable since they are already using VSCode.

The difference between Arduino's IDE and PlatformIO come down to installing board support and libraries. Arduino's IDE is probably better if you are using Arduino libraries on a board that it directly supports since the installation process will be nominally easier. If that isn't the case, PlatformIO will likely be significantly easier since it supports more board, frameworks, and libraries.

I only used the VScode extension and is great. Except that it modifies the whole interface so I have two IDE instances one for with platformio and one without. It even encouraged me to write test for my arduino projects

Its been a while but I think I just hit install on the extension in vscode. It was pretty easy.

PlatformIO is 3 feet from gold. I still use Arduino IDE, it's a few clicks to get up and running.