How can you say that it failed you when you got Astolfo! D:
Because Astolfo is simply put, not good.
He's in short a downgraded overglorified Medusa with a gold border who people only use and defend for the sake of being a trap.
Both of them are Quick-based AoE Riders with similar kits in their skills, they both have Monstrous Strength, a stunning skill and a skill that charges their NP bars.
So, what does make Medusa decent while Astolfo is inferior? Consistency.
Medusa's Monstrous Strength is a rank superior to Astolfo, who for a SR, has a very low ATK. Her Mystic Eyes have a much better chance of stunning the opponent than his Down with a Touch. Astolfo's third skill is his only pseudo-saving grace, but is also his worst skill, it gives him 50% NP charge, compared to Medusa's third skill that only gives her 20%. The problem comes in that it has a secondary effect, which gives him either star absorption, generation or critical hit up at random, making him inconsistent.
Besides that, he along Lancelot and Atalanta from the Terrible Quick-Based NP Gain trio
only the other two are actually usable beyond that. Yes, he can get a whooping NP charge with a skill, but...if you want to use it again, you'll have to wait various turns for the cooldown. This is where Medusa being more consistent than him comes again, she has a much more decent NP gain and 2 Arts cards, not to mention her third skill actually gives her a higher NP gain. As such, you can use her NP more often than his.
And again, he has low ATK for a SR, so you won't get whooping damage from his. He does have a superior Magic Resistance and Independent Action over her, but the former doesn't matters as with any Magic Resistance and with how inconsistent he is, Medusa puts her Independent Action to better use.
I short, what he can do, someone of a lower rarity who is easier to upgrade does it better. Sure, he's got the whole 50% NP charge thing, but besides that...There's no reason why to choose him over her, or better yet Drake who many people have in their friend lists and is better than the two.