The best champs outside of lane to counter Bel'Veth include Kalista, Samira, and Lucian. These champions are all great at countering Bel'Veth with high win rates over 60%. Even if these Bel'Veth counter picks are not picked in the same position as you, it's not a good idea to take them into any of these matchups. They will very likely crush Bel'Veth.
Yet, if the other team brings either Rumble or Ziggs, Bel'Veth mains should strongly think about selecting them, as they easily wins against these champions with win rates over 55% against both ofthem.