> I think neovim would do better if they started integrating the core plugins like LSP, tree sitter

That's exactly what they're doing.

Both tree-sitter and LSP are built in and the primary LSP/tree-sitter plugins only bundle default LSP configurations and tree-sitter queries respectively. They're also planning to include tree-sitter query bundling into Neovim natively somehow, to make it even less reliant on the nvim-treesitter plugin.

They recently simplified the LSP configuration and to configure a new LSP you basically do this:

    vim.lsp.config("expert", {
      cmd = { "expert" },
      root_markers = { "mix.exs", ".git" },
      filetypes = { "elixir", "eelixir", "heex" },
    })

    vim.lsp.enable("expert")

> And then in the "LspAttach" autocmd you can define your LSP specific keymaps for example.

If you want. It also now ships with most auto-mapped.