That is default jshint message. To avoid this, use jshint es6 option to ignore such warnings, add this to beginning of a file:
/*jshint esversion: 6 */
Actually, those warnings on left - is just for information. They don't restrict you to do anything and write your js any way you want. It is just visual clues.
We will consider adding global option to disable jshint in IDE.
Nothing dictates anything here. We "recommend" certain style for benefit of all potential users of content made in playcanvas. You can write code the way you want. Nothing enforces you to write in any particular way.
Nothing expected of you. "easy to fix", interpret as: "we've noted the issue, and expect the fix soon". We do not provide any timelines on things, unless it is a critical issue that stops users from being able to work.
I'm actually easy-and fine with feedback you provide. Really - it is useful. Nothing taken emotionally
We want to ensure users actually having fun, and not frustration while trying to learn new tool. Which means we have work to do on that ground.
Thank you again for a feedback!