She's less of a 1:1 character rip off. Sure, she has a lot of superficial similarities (Has a tiny familiar, loli, magic usage and consequences from over use of it, etc.) but Megumin isn't actually involved with the demon army (the demon king is its own thing to my knowledge if I remember correctly) nor is she a former general like Wiz is. Also Megumin isn't secretly a lovecraftain horror known for eating people.
Sure, there's definitely trope-y aspects to both of them, they both are parody characters, but she's not as blatantly ripped off and they don't have similar personalities at all.
@Goretantath