CoPilot has been working fairly well for me in GoLand. I don't know if Copilot has the same or more support in Goland than in Webstorm/Pycharm, so, if the latter, my observation might well be disjoint from yours.
But so far, it's a moderately capable assistant. My biggest complaints with it have more to do with its responses than its fit with the IDE.
Copilot in VS Code has model options, the new agent is available in VSC Insiders that will implement full features and show it's changes in a diff viewer. Jetbrain IDEs don't have the option to change models
And their default model is pretty bad in JS/TS world. (but great in C#)
Copilot works great for every language but the plugin integration into JetBrains IDEs is not as deep.
But so far, it's a moderately capable assistant. My biggest complaints with it have more to do with its responses than its fit with the IDE.