I'm sorry but this seems really strange to me. Are you suggesting we should try to not be the top GNP civ because we'll be attacked for it? If people will team up against the top GNP civ because they're a threat, then they'll team up against the top MFG civ because they're a threat by the same logic. As a high GNP producer we make ourselves a valuable partner for tech trading, and like others have said if we get those critical military units sooner we can have a period of time where a small number of units can decimate the larger but less well equipped armies of our opponents.
Also it may be worthwhile to note that nobody knows who the top GNP civ is yet, we're anonymous and will remain so unless we develop a large tech lead that they can see after alphabet, or if we open borders with our opponents and let them come in to see our capital.