Jacob is expensive for what he provides, and he is hard to protect. But if properly supported, he can be a big, valuable cannon. If you can get your magic up to 10, you get a massive 7 ranged attack. In some matches, you can do this. Often, you can discard aggressively to feed his Radiant Shot, knowing you can bring those discarded cards back with Sera.
If the opponent’s faction isn’t pressuring you to hurry up and you have time to build up the whole setup for him, he can be quite strong, but identifying those games is not easy. Six life is not much, but with Citadel Knights and healing, it can feel endless.