completely... disagree...
Meganium is perhaps the only grass type who stands a chance against flying because it knows counter. With counter on Meganium plus healing moves it can drive Zapdos nuts.
With reflect and light screen it can stall out more PP than a lot of other Pokemon can in GSC days. Even in RS now it's still an annoying one to fight against. With both of these strategical moves it can last a lot longer than any other grass types can, only lower than Celebi (due to heal bell, recover and legendary stats).
I'll rather use Meganium as a physical attacker for grass type. With Earthquake it got pretty good potential (btw it can knock out Vileplume and Venusaur much faster than the other 2 can knock out Meganium even if they have Sludgebomb which is never really recommanded.) Body Slam is always annoying due to paralyzation. Can also learn ancientpower which gives some opponent quite a shock. With the great varieties for its movepool Meganium's moveset is rather unpredicatble. Is it going to to stalling, or a countering Meganium?
Meganium is certainly not a Pokemon only if you want a challenge for the ingame (well the ingame can never gives challenge to anyone sadly). It has just as much potential as all other starters.