Neovim has a built-in language server (ALE and others do the same in other editors) and since it's based on the spec that VS Code put forth, the autocomplete and features are basically identical as is any go-to-definition. Debugging in a tmux split is, in fact, "fine" which is really all you need. I'm not sure what build system integration means--my editor is agnostic to the build system and I would hope it stays that way.
If you're asking for your editor to run a browser window under its hood and chew up your battery for tooltips on mouse hover instead of inputting a short key macro on cursor, then I don't know what to tell you.
If you're asking for your editor to run a browser window under its hood and chew up your battery for tooltips on mouse hover instead of inputting a short key macro on cursor, then I don't know what to tell you.