For the reasons you stated. Psion, whilst only 5 mana, drains this from all enemies so is more useful. Spider Queen does as many things as the Manticore (Webs, full drain, massive armour debuff vs Stun, 7 mana drain now, Attack self buff) which are just as useful.
What set Manitcore apart from Cockatrice, Succubus and Spider Queen was the combination of traits namely Empowered and Impervious and the usefulness of the attack buff on offence and which the AI can’t balls up when on defence.
That is why it was being used far more than the other mana drainers which all have the same cost, 9 mana, as Manticore. Also, I believe it having empowered generates the ‘feeling’ that it’s always draining your mana.
I’ve not been playing this game long but when I first started out I’m like ok this is a nice game and basically stopped playing yugiho, but after this last manticore buff and what most know what has to be goin on in pvp with a lot of the top 10 ppl most that has to be cheating this game is started to remind me why I slowed from playing yugiho and its banned list, they don’t touch the real top treats like Khorvash, famine who is just really over powered or the cheaters but rush to do something to a troop like manticore that’s only an issue to the ones that want it easy. I cant even get some of them troops that’s really over powered cause I’m low leveled like Khorvash, famine but I have to fight against them at less with manticore I had somewhat of a chance now that’s gone not to mention by being low leveled getting the real high powered troops traits is like almost impossible and I’m not spending money for it so once again thanks dev’s for caving in to all the whiners