Lilyth (Summer) is an earth element ranged damage dealer. Since she was released about a year ago in JP, her abilities are somewhat outdated, leaving her with many negatives than positive and can struggle to compete with the current units.
Lack of TP skills hurts AP gain, especially compared to other rangers with a damage increasing TP buff. Negative slash and magic resist, which are somewhat common in PvE and PvP. Master ability doesn't provide team buffs, but instead upgrades her Barrage to have guaranteed hit ability with no AP reduction. 1 less range compared to units with a Ranger and Sniper sub job, but can be offset if you use her TMR buff instead of something like Illusory Bell.
Her EX upgrades gives her some increased survivability, but it's only useful if you don't use a tank on your team. The job lvl 25 new skill can be considered her saving grace since the ability to reduce enemy's DEF is quite useful against bosses, but it only lasts for 1 turn.