I like the idea of a cleric, but I don't think we need to remove abilities from the conjurer. I think that the conjurer is similar to a red mage--well rounded in the variety of magic, but not particularly strong in any one area. Having low level healing and elemental magic fits that well.

The only problem I see with the Cleric as you've laid it out is that it would be very challenging to play solo. Perhaps add light/holy magic to the cleric as a way of adding some level of attack power. It could also be a buffing class as well, so time magic could be thrown into the mix. Then Thaum could be a debuffing class + dark magic (meteor, etc.)

I think SE also needs to add a summoner and a blue mage to the mix as well and we'd have a variety of mage classes to choose from.