Ixehl's infect strategy is secondary to a more mid-range play that is playing your opponents' spells
Exiling creatures to make 4/4 zombies is already strong, but it gets better when combined with mill engines like Lord Xander, the Collector or Phenax, God of Deception
Sure, its one turn slower, but it also gives tokens right away, so it balances out
Any enters abilities of the copied creature will trigger when the token enters the battlefield
A 5/4 for 6 generic mana is actually fair, but that's no longer good enough for players, even in Limited
In a way, its a little strange that we can have spaceships travelling between planets alongside the traditional convention of planeswalkers literally striding between realms of existence