You severely underestimate how much powerful a permanent ATK drop to 0 can be, especially when it's a monster effect from the hand. There's a reason why handtraps flourish in OCG/TCG: it's not easy to counter.
Only thing holding Lamia back (and arguably a very severe drawback), is the need to use Reptiles, as there aren't any good Reptile deck to use Lamia with, even today.
Your mention of handtraps is irrelevant. Lamia is not a hand trap. The reason hand traps are good is because they disrupt the opponent's plays. Lamia's effect is not a Quick Effect, it doesn't interact with your opponent's plays whatsoever.
Monsters with ignition effects are not hand traps. (Granted, it's a fan-term, but the whole point of hand traps being special is responding to the opponent's plays. A card like Lamia, Electric Virus or Thunder Dragon doesn't do that.)
Anoymous
not KoG
