I don't agree with letting the devs off the hook for creating a terrible product. The Civ IV AI played well and that was with computer technology that was 1/10 of what people have today. It's just poor planning and development by Firaxis and of course the 1 upt system.
The Civ IV AI was terrible. Also, Civ IV was a far less complex game than is Civ VI. Let's be honest about this. For the foreseeable future, AI is always going to need bonuses to be remotely competitive with human players. Most players aren't willing to sit around for 3-5 minutes every turn while the AI makes its moves.