Margaret isn’t bad; she’s a very good tool for a specific purpose. Think about her like an Allen wrench: you don’t need it every day, but when you do need it, it’s really really helpful to have.
Miki is like that too, only he’s more like a pneumatic jackhammer for titans: great if you need to blow through something, but not so good for helping out with the planting in the garden. And since you DO hit titans every day, he’s way more useful overall than Margaret.
The heroes people consider the “best” generally either excel incredibly at one thing (Guin), or are very good at everything (GM).
The heroes who are specific tools like Perseus (counter healing) and Margaret (counter sniper) don’t get much love.
Thoth-Amun, on the other hand, doesn’t really have a role that he excels at in my mind. He doesn’t buff, he doesn’t debuff, he doesn’t protect anyone else, and he doesn’t do much damage. He is probably the objectively weakest of the HOTM now that Aegir is no longer actively destroying his flanks.