That amount of mass will push the arm/stylus resonant frequency down too low making the system unstably sensitive to external vibrations.
Expanding on what Kr4 said, the ideal tonearm effective mass depends on which cartridge you mount on it. The cartridge's own mass affects the calculation. The compliance of the cartridge's suspension is an even larger factor.
So there's no simple answer. A tonearm is one half of a mechanical system that includes the cartridge. Without knowing the parameters of one half it's impossible to optimize the other.
One interesting concept relating to your question is the idea of differentiating between moving mass in the vertical vs. horizontal planes. High mass in the vertical plane is very bad for negotiating warps. High mass in the horizontal plane can, depending on the cartridge, help the arm resist deflection and improve bass and dynamics (just as you supposed). This is the theory behind the Dynavector tonearm. Look it up. Read the Strange Tonearm Tweak thread for a thorough education.