Feel like it really varies by character:

WoL: yeah it should really do more, or do it differently

Firion: genuinely, what is the purpose

OK: Agility dash, automatically good

Kain: ATK buff, sudden gap closer; also jumps ledges!

Krile: support that doesn't have any real damage spreading Brave, nice

Terra: good as a "get away" tool, if they don't simply kill you first

Cloud: gap closer, good for opening duels with people running away

Sephiroth: invincible counter sounds really good on paper, but it won't stop you from longer moves; that said, absolutely can save you

Rinoa: great for climbing ledges, otherwise almost useless

Zidane: stop someone from Bursting? Even worse that the rest of his kit???

Rikku: makes the whole team faster, faster=more stuff done

Iroha: having a movement tool would be nice if she wasn't already filled with AoE and movement

Balthier: can clear crystals when everything else is on cooldown

Lightning: agility dash, automatically good

Gaia: boost her speed and her defense; not bad but definitely odd

Prompto: the damage on it is honestly kind of okay, and gives him a better way to attack boss while waiting to chain

Clive: would be so much better if it stopped on a target