and what if this restriction was lifted? how gameplay would change?
Let's see , it would make tradition stronger , I agree.
you could then have a strong faith based play alongside the military one and the science oriented one.
You would have more choice involving faith even if you generate a lot through your pantheon , since you'd want 1k faith for an engineer as well as the two prophets , thus making a rush to theology a bit more attractive.
It would also reinforce piety as a secondary tree , you could viably delay rationalism to get a stronger faith generating religion and balance your faith costs , thus going for a viable snatch wonders strategy at the cost of a bit of science , this would be refreshingly good to have something new to do since I abhorre piety as it is right now, and since gogin for too much wonders early to mid game only hinders you as it is right now.
But all of those good aspect are still not good enough to justify tradition being even more OP.
I would reject the idea in the game as it is , but it still could be a lead into another way of playing ,provided someone better than me at game design would rethink faith costs,tradition and piety.