**bump

Can't you just use:

Route::get('/', ['as' => 'home', 'uses' => 'HomeController@guest']);

Route::group(['middleware' => 'auth'], function () {
    Route::get('/', ['as' => 'home', 'uses' => 'HomeController@auth']);
});

middle-ware

Do it in a Controller maybe?

<?php

namespace App\Http\Controllers;

use Illuminate\Http\Request;
use Illuminate\Support\Facades\Auth;

class HomeController extends Controller
{
    function __construct()
    {
        $this->middleware('auth', ['except' => 'getIndex']);
    }

    public function getIndex(Request $request)
    {
        if (Auth::guest()) {
            return view('welcome');
        }
        
        return view('dashboard');
    }
}