Unless something's changed, every AI-backed language server I've tried in Helix suffers from the same limitation when it comes to completions: Suggestions aren't shown until the last language server has responded or timed-out. Your slowest language server determines how long you'll be waiting.

The only project I know of that recognizes this is https://github.com/SilasMarvin/lsp-ai, which pivoted away from completions to chat interactions via code actions.