Basically if an enemy unit is in an engineer radar's area of effect, any outgoing mic chat/team chat can be heard by the engineer owner or guys in owners squad or commander.You may think its cheap but it serves both sides as the clever enemy can say that they are commencing tank rushes into a certain area while the tanks went for another area. It also means that players may not have knowledge of the radars so they let something slip.Imagine if an engineer got to the point of getting the enemy commander in that radar, then it just creates a whole new system of intelligence and engineers will be useful.
The engineer doesn't need more versatility/buffs. How about giving a skill that gives the scout a small radius to hear shit?