Is Jolteon still worth using competitively?

130 base speed still carries it. it outspeeds a lot of what it wants to hit without needing any setup. just don't expect it to take a hit, it's frail on both sides.

In the lower singles tiers, sure. It's fast enough to Volt Switch out of bad matchups, and that's most of its job. In VGC there are just better electric types now.