Not to be that guy, but I think the issue with Sinbad is that you're giving him mounts of animals he met, not rode. He never tamed the Leviathan, the Roc, or the elephant king. It'd be like if Hercules could summon the Nemean Lion and ride on that. Or if Artoria could ride a Dragon. Just because they met or fought something, doesn't mean they're gonna be riding it.