Bane is a very solid spell, but is better on a character that's both in position to cast it (close enough to the action) and has invested in Concentration maintenance (items, consumables, CON Resilience, War Caster, maybe even some class abilities?) to keep it up once you get there. Not really Rogue's focus, at least the way I'm playing him. Same reason Color Spray got swapped out on my AT Astarion. Spray and Sleep are both no save so good for non-casters. They go by current hit points so can finish off mobs that are low without needing a roll, and sometimes multiples. But Spray also requires being in melee which my Rogue often isn't to get benefit from High Ground and ease of Bonus Hide.
Rogue's focus is position and sneak attack. In the case of assassin also surprise or at least best your enemies on initiative rolls.
Extra action with haste or potion of speed is kind of... lackluster though. You can only sneak attack once after all, and the rest of the useful stuff is a bonus action for rogues(disengage, dash, hide, etc). Just using it for a regular attack is ok but I want other options.
I think having Bane as an option for bigger fights might fill that gap, at least for a round(you only cast it once and then try to mantain concentration). My durge is to have somewhat high wisdom and constitution anyway(including wis save proficiency through resilient feat).
It is the cost of a feat that is somewhat high, but the spell is good and you get two decent cantrips with it. I wonder how many spells you can learn through events(such as speak with dead and danse macabre with necronomicon thingy).
