For RD you need three entities: tf_logic_robot_destruction; here's where you'd set things like the amount of points needed to win and the amount of robots that can be active at any one time. tf_robot_destruction_spawn_group; which controls bot respawn time and what team they're on. And tf_robot_destruction_robot_spawn which is placed at the spot you want robots to spawn and controls robot health and how many points they drop. These entities are required on top of things like team_round_timers, tf_gamerules, whatever else your map needs. You need all three entities for robots to spawn.
To recreate the bot tiers Asteroid has, you will need to create six tf_robot_destruction_spawn_groups - three for each team, one for each type - and six tf_robot_destruction_spawns - one for each tf_robot_destruction_spawn_group.