If you're not running a Slann, the Engine starts to look a lot more practical. A level 2 skink with Engine and the Plaque of Tepok is for all intents and purposes a level 3 wizard. That, combined with the cool effects of the Engine itself, can make for an impressive magic phase.
And let's not forget the ancient stegadon. It can be fantastic combat unit on it's own when used correctly- basically you've traded the giant blowpipes for the Engine effects.
It's not without its drawbacks. The setup above costs more than a BSB Slann with three disciplines- purely on magical terms the Slann wins hands down. You also don't have anything close to the protection of a Slann; even without temple guard, the Slann can have a 2+ ward against a cannonball (or ignore it completely), a cannonball which stands a very good chance of killing your skink priest -and possibly mount- outright.
Pros:
Strongest magic we can get without a Slann
Burning Alignment kills multiple small units and lone characters well
Bubble wardsave can be your your best friend against long range shooting
Stegadon charge! Burning Alignment followed by Impact hits have slain many a greater daemon for me
Cons:
Hugely expensive!
Instant war machine & shooting magnet
No choice of magic lore
Skink Priest is vulnerable in combat- especially to challenges
Basically, if all you want is stronger magic for your Carnosaur army, you might be better off with just a couple skink priests on foot, with a few helpful items. Double casting the Heavens signature spell is a combat winner for sure if you can pull it off.
If, however, you want a stegadon that also does strong magic support, and have the points to do it, the Engine may be the way to go. You're going to have to alter your play style to support it, but it can be devastating when used right.