The greatest champs outside of lane to counter 披甲龙龟 include 残月之肃, 麦林炮手, and 暴走萝莉. These champs are all good at countering 披甲龙龟 with decent win rates over 58%. Even if these 披甲龙龟 counter picks are not chosen opposite your position, it's not a good idea to take him into one of these matchups. They will very likely beat 披甲龙龟.
Yet, if the other team brings either 诺克萨斯统领 or 爆破鬼才, 披甲龙龟 mains should seriously consider picking him, as he easily dominates these champions with win rates over 54% against each ofthem.