Joltik is okay, but it's outclassed both by other Bug types and other Electric types. It's a Bug type, and Bug types aren't too good in LC at the present. It's fast, but outsped by many threats, like Scorbunny, Onix, and Archen. All can easily take out Joltik within one or two hits, as Joltik doesn't often run Eviolite. Scorbunny absolutely murders it with Blaze Kick, Archen squashes it with Head Smash, and while it has Giga Drain, Onix is faster and can take it out with Rock Blast while staying alive thanks to Sturdy. Joltik is weak to Stealth Rock, and using Heavy-Duty Boots means you can't use something like a Life Orb.
In comparison to other Bug types, Joltik finds a small niche as the best special attacker out of any of them, but special Bug types aren't exactly in large demand in the current metagame. Anorith is a better physical attacker, with Swords Dance, Hone Claws, and Swift Swim, while Dewpider is better defensively, with Sticky Web and more bulk.
In comparison to other Electric types, Joltik is not even close to the best. Magnemite resists Flying, it's a special attacker, and it can pull Berry Juice + Sturdy + Recycle shenanigans to annoy an opponent. Elekid is even faster than Joltik, boasts a higher Special Attack, and gets moves like Psychic, Ice Punch, and Brick Break.
Now, Joltik isn't necessarily bad. It's able to take out slower threats like Mareanie, sometimes Pawniard, and non-Eviolite Timburr, but it still struggles. It's too frail, weak to Stealth Rock, outclassed by Magnemite and Elekid, and its Special Attack, while good, isn't the greatest. It's okay as a Bug special attacker, but as I said, those aren't very popular at the present.
Hope I helped!