After spending 2 hours, digging through google and Laravel source, I came up with this solution, which I think works the best and looks the cleanest. No need for redirects and multiple inner requests.

You add this route at the very bottom of routes files. If no other routes are matched, this is executed. In the closure, you decide which controller and action to execute. The best part is - all route parameters are passed to action, and method injection still works. The ControllerDispatcer line is from Laravel Route(r?) class.

My example would handle 2 cases - first checks if user exists by that name, then checks if an article can be found by the slug.

    Route::get('{slug}/{slug2?}', function ($slug) {
        $class = false;
        $action = false;

        $user = UserModel::where('slug', $slug)->first();
        if ($user) {
            $class = UserController::class;
            $action = 'userProfile';
        }

        if (!$class) {
            $article = ArticleModel::where('slug', $slug)->first();
            if ($article) {
                $class = ArticleController::class;
                $action = 'index';
            }
        }

        if ($class) {
            $route = app(\Illuminate\Routing\Route::class);
            $request = app(\Illuminate\Http\Request::class);
            $router = app(\Illuminate\Routing\Router::class);
            $container = app(\Illuminate\Container\Container::class);
            return (new ControllerDispatcher($router, $container))->dispatch($route, $request, $class, $action);
        }
        
        // Some fallback to 404
        throw new NotFoundHttpException;
    });

Hope this helps!