The effect surely can be a gamechanger but the problem of cards with tap effect is that there are too 'slow' because they need to stay 1 round on the field without making an instant impact like CIP cards. And there are a lot of cards who counters this cards really hard (like pit and corile). And waste 6 mana is hard too.
On the other hand if you can use his effect he gives you huge advantage on field and hand control. He can kill for example magris and loco and can prevent enemy draw (and bait for craze) and discard.
And with 5000 he isnt easy to beat.
AND i think he is a good bait to thin out strong removal cards (like pit) and to clear the way for Bolmeteus.