Sunny was not powerful enough to casually slay a Corrupted Tyrant... yet. Defeating one was not outside the realm of possibility for him anymore, but it would require a good amount of meticulous study and preparation. Even then, challenging a Nightmare Creature of such immense power meant dire risk to his life.
However, Sunny did not really need to kill the jade beetle.
All he really needed to do was to break the balance of power between the monstrous Tyrant and Sky Tide.
Something like that was more easily said than done, but Sunny had several advantages that very few people possessed. He had a bow created by the best forgemasters of the great clan Valor, or maybe even King Anvil himself. That bow demanded immense strength to be drawn, but was capable of sending arrows much further, and imbued them with much greater force.