No. Meganium is a defensive/support Pokemon, and so its best if it plays that role.
Reflect/sunny day- sunny is perfect for synthesis cuz you recover huge HP
Light screen-boost special defence quite a lot
Giga drain/energyball- so it can still attack and wont be destroyed by taunt
Synthesis- mega annoying expecially after the suns influence.
A more deadly/offensive meganium should have modest nature or quite
Moveset: sunny day- boost fire type moves and doubles the effects of growth.
Growth- boost attack+SP attack by one stage; however with the sun out it boosts the Attack and special attack by two stages (thats the same as using sworddance and nasty plot in one turn).
Solarbeam/giga drain- depends if you prefer longevity over raw power.
bodyslam/earthquake- bodyslam gives nice coverage and threat of parlaysis. Earthquake- great against fire and poison type Pokemon and with growth+sunny day boost your earthquakes, solarbeam/giga drain and bodyslam your attack are horrifingly deadly