Tempest clerics getting to do a push when dealing lightning damage could actually be slightly broken.
The PHB description of Thunderbolt Strike is:
At 6th level, when you deal lightning damage to a Large or smaller creature, you can also push it up to 10 feet away from you.
It doesn't say anything about how you deal the lightning damage or how many times per turn you can do it. Just deal lightning damage, hand out a push. There's also no mention of a save against the push.
And moving enemies around is quite broken, particularly with the verticality in BG3. I'm not sure it is strictly speaking "better" than light domain, which turns into a well armoured fireball-blaster with good health at level 5, but it does sound fun. And just a little bit broken.
I think the brokeness really depends on access to lightning damage. For sure the rebuke style reaction would be great for pushing away attackers when you need to bail, but it is probably going to be limited use. If it was thunder or lightning damage, that would be a game changer, but I think they wanted to keep the thunderwave shenanigans to a minimum.
