649 Genesect

Fury Cutter is recommended for its superior energy generation, which lets it utilize is cheap charge moves more frequently. Metal Claw offers slightly more damage output, but the trade-off in terms of energy gains, and Steel-typing's poor offensive value, makes it the inferior choice overall. 

X-Scissor costs the least amount of energy, benefits from STAB, and can be spammed often. Magnet Bomb offers some extra coverage, and in neutral fights can deal surprising amounts of damage with STAB. Hyper Beam is among the most expensive charge moves in the game energy-wise, and is not recommended due to the risk of being shielded, in addition to not benefiting from neither STAB nor a Super Effective multiplier. 

Genesect is a Bug/Steel Pokemon with high offensive stats, relatively poor bulk, and a spammy moveset. Due to the CP cap of Great League, Genesect's performance very closely resembles that of Scizor, another Pokemon with the same typing, very similar stat distribution, and almost identical movesets. To compare between the two, Genesect sports the superior Steel-type charge move, while Scizor features the superior Steel-type fast move. However, in the Great League meta these features are not typically valued due to Genesect's poor bulk, and very niche coverage. Some Pokemon that are considered to be very bulky in this league can overcome Genesect, even when Genesect would have a typing advantage. Overall this is probably a Pokemon you can pass on, especially considering the large resource costs needed to unlock its secondary charge move. 

Access to quick Bug and Steel coverage in addition to Bug/Steel-type resistances gives Genesect a good niche in Ultra League. Wins against popular Fairy-types and advantages against bulky Psychic-types are definitely a welcoming addition to anyone's team, but struggles against the rest of the meta results in Genesect being more questionable than favorable. 

With a max CP of 3353 and somewhat poor bulk, Genesect would appreciate additional stats to compete with the top Pokemon in this league. Unfortunately its Bug and Steel coverage is almost useless in this league, where Dragons and Steel-types are ubiquitous. It gets some points for being able to beat Fairy-types, but it doesn't get much better beyond that when it comes to the popular meta.