Looking at the documentation and an issue raised on the their Github issues section, your solution seems to be the best. Some methods allow you to specify the gender for a name so you could do like this:

$gender = $faker->randomElement(['male', 'female']);

return [
    'name' => $faker->name($gender),
    'email' => $faker->safeEmail,
    'username' => $faker->userName,
    'phone' => $faker->phoneNumber,
    'gender' => $gender,
    'address' => $faker->address,
    'dob' => $faker->date($format = 'Y-m-d', $max = 'now'),
    'password' => bcrypt('secret')
];

Hopefully this fits your requirement.

Since model factories create in-memory objects, because of big memory usages it is not suitable for large seeds.

But you can use Faker for data generation:

use Faker\Generator as Faker;
class PostSeeder extends Seeder
{
    public function run(Faker $faker)
    {
        $users= collect(User::all()->modelKeys());
        $data = [];

        for ($i = 0; $i < 100000; $i++) {
            $data[] = [
                'body' => $faker->text,
                'image' => $faker->imageUrl(),
                'user_id' => $users->random(),
                'created_at' => now()->toDateTimeString(),
                'updated_at' => now()->toDateTimeString(),
            ];
        }

        $chunks = array_chunk($data, 10000);

        foreach ($chunks as $chunk) {
            Post::insert($chunk);
        }
    }
}