Grass-type Pokemon are typically underrated and for a good reason due to some underwhelming creatures in the category.
Not every Grass-type Pokemon can be like Venusaur or Sceptile. These are the cream of the crop and stand out among the normal Grass-types that often go overlooked.
The Hoenn region did not add a ton to the Pokedex, but it did deliver a decent list of new Grass-type Pokemon. A few of them could have easily shone, but ended up being rather underwhelming.
3 most underwhelming Grass Pokemon in Hoenn
#3 - Tropius
Tropius gives off Meganium vibes. It looks like the final evolution of a Grass-type starter Pokemon. Unfortunately, its appearance is the only thing that matches the levels of a powerful Grass-type.
It does have a secondary Flying-typing, but that makes it even more susceptible to Ice-type attacks. 99 base HP is pretty solid, but the rest of its stats are very underwhelming.
#2 - Shiftry
Hoenn saw a large experiment of giving Pokemon two types, with a popular combination being Grass/Dark. Shiftry has a good Attack and decent Speed, but there are many Pokemon without the added weaknesses the Dark-type brings.
Nuzleaf needs a Leaf Stone to evolve into Shiftry, as well, so it would be better to save it and use it on Gloom to obtain a Vileplume. Shiftry isn't all that special.
#1 - Cacturne
Continuing with the Grass/Dark-type Pokemon trend is Cacturne. It has great Special Attack and Attack, both at 115. Typically Pokemon with even stats like that don't have good stats elsewhere.
That is especially true for Cacturne. It has horrible defenses and a base Speed of only 55. Weaknesses to Fighting, Poison, Fire, Bug, Flying, Ice, and eventually Fairy, are sure to see it struck down by a much quicker opponent.