Insuperable means 'insurmountable' or 'unbeatable'. It's a strong adjective used to describe something that cannot be overcome or surpassed.
In
Most breakup songs beg. This one gloats. Carín León opens by measuring how far he still has to go, "Ya estoy así de poder superarte" ("I'm this close to getting over you"), and then turns the same ruler on her: "En cambio, a ti te cuelga pa' olvidarme" ("but you, you're struggling to forget me"). The whole song runs on that gap. He is nearly free. She is not.
Then it gets properly cocky. "Puedes fingir que no me extrañas, pero el truco no te sale" ("you can pretend you don't miss me, but you can't pull it off") is the kind of thing you only say when you are certain, and "Puedo encontrarte un reemplazo" ("I can find a replacement for you") is a bit much even for a man this pleased with himself. He cannot resist an I-told-you-so either: "Bien te lo dije, 'Ponte pilas', pero no me hiciste caso" ("I told you, 'Get it together', but you didn't listen"). The chorus stops arguing and reads out a result instead, and "¿quién tenía la razón?" ("so who was right?") gets its answer straight from the title: "fui y siempre seré el mejor" ("I was and always will be the best").