You do have a point there akhi. God can be one only and even a child will understand that. The trouble is that when you talk to a grown up Christian he will accept none of your arguments in favour of Tauheed. There lies the crux. Islam has to be communicated to Christians and they do have entrenched thoughts.
He is indeed better than Zakir Naik. As far as Ahmed Deedat is concerned then we should not forget that he is the father of the genre. (Of course real father would be Maulana Rehamtullah Kairanwi).