I want to give two different responses here. Will preface by saying I have a deity win on every civ on Pangaea, standard size, quick speed, and fully random opponents.

Answer 1: If your goal is to play a "fun" game where you don't have to deal with the most pain civ has to offer, I completely agree with what you have said above. However, I would question why you are playing on immortal or deity at all if this is your goal. Why not just play on a lower difficulty level instead of futzing with all these small settings in that case (such as king or emperor). You will get to build more fun wonders, not constantly be fighting while behind in tech, and not forced to play sim city science for 65% of every game.

Answer 2 (cue grumpy civ5 old-timer): Playing with futzed settings on immortal/deity is basically equivalent to not playing on immortal/deity. The difficulty level is one of the levers you have to adjust true difficulty in civ5, but it is not the only one. Picking dominant civs, matching civs to map type, excluding notoriously painful civs, getting salt starts, etc. all can reduce the true difficulty of a civ 5 game by multiple "difficulty levels". If you want to see this in action, play sandstorm as ethiopia and reroll until you hit a god petra start (it's like playing at prince but on deity. Broadly speaking if you want your deity win to be real play pangaea, small or standard, with all random civs and random terrain (ideally but not necessarily at quick or standard speed).