0652 Chesnaught

Vine Whip is generally recommended for its significantly faster energy generation, as well as benefiting from STAB. Smack Down gives up faster energy gains for strong Rock-type damage, though it doesn't get STAB. Low Kick is a poor move. 

Superpower is a very strong move in PvP, offering very high damage for its low energy cost, but is risky to use with its self-debuff. Frenzy Plant is an insanely powerful attack, offering consistent high STAB damage at a fairly low cost. Energy Ball is a far inferior move in comparison. Gyro Ball requires more energy, lacks STAB, and its coverage isn't as useful. Solar Beam demands the most amount of energy, making it undesirable to use. 

Chesnaught brings a fairly unique perspective into the Great League meta, with access to both Grass and Fighting-type coverage. While this isn't particularly unique, its moveset synergizes better than that of Gallade and competes with Sirfetch'd quite closely. A combination of Vine Whip, Frenzy Plant, and Superpower offers devastating potential. Chesnaught's type combination also provides it with a rare resistance to both Ground- and Rock-type attacks, allowing it to completely wall the omnipresent Galarian Stunfisk. Chesnaught, however, is held back by its average bulk and its six weaknesses (notably being doubly weak to Flying, a common type), and may struggle to stand out among existing Grass-type Pokemon as a result.

In Ultra League, Chesnaught faces a direct competitor: Virizion. Virizion's moveset is similarly excellent, but is more flexible and can even threaten Flying-type Pokemon. Although Chesnaught is not a terrible choice by any means, it has trouble standing out as a result. However, Chesnaught can find play in Premier Cup, where legendaries are banned.

Realistically only viable in Premier Cup, where it can function as a corebreaker to Gyarados + Excadrill. In the Open Master League, Chenaught's stats are underwhelming. The already niche Virizion is superior in every way - it has more stats and a more reliable moveset.