Yeah no. Immortal and Deity AI's get a lot of free stuff and yield modifiers that are unfun to play against. Playing against 12 opponents, all of which cheat. Only 1 or, if you're lucky, two strategies work against that, all of them involving forgoing fun peace building and attacking aggressively in the Ancient Era and Classical Era. Hard, hard pass.
Emperor is my upper limit and I don't even like playing Emperor (with most Civs anyway, and since I usually roll my Civ at random...)
I agree with the sentiment, it actually hits pretty close to one of my philosophies about difficulty levels, but I think you're approach takes this to far:
I believe that as a turn-based strategy game, increasing the difficulty level doesn't make the game harder; rather it limits the number of viable strategies that will be successful. When you're playing a first-person shooter, increasing the difficulty level makes the opponents move faster, have smaller hit boxes, shoot more often and accurately, your shots do less damage and their shots do more damage to you. This makes the game harder. But as a turn-based strategy game, having the opposition be front-loaded with lots of extra units (and consequently cities) as well as difficulty multipliers to their various yield accumulations forces you to compensate by prioritizing some options (which you don't find fun) over other options (which you'd prefer.) Consequently, playing at higher difficulty levels means that many of your creative approaches will not be successful and you fall into at least some degree of rinse/repeat playing, which really kills the replay value of the game.
That said, I'm not the best player on this forum. By far. But I have won deity in all four of the original main victory conditions with civs that are poorly suited towards that victory condition, and all before turn 240. However, I prefer to play deity very rarely because I enjoy the game more on lower levels. Here's my very generalized interpretation of the difficulty levels:
Prince and below: only for players who are just learning the fundamentals of the game.
King: for players who know the fundamentals but haven't yet learned how to implement them effectively. Also for experimenting with new "unproven" tactics and strategies - Doing so at lower difficulties may give false impressions and conclusions as the AI's limitations make them uncompetitive. At King, they're at least trying but put up little resistance (which is the source of your main concern.)
Emperor (no barbs): for when a proficient player wants to play a game where everything works out the way they planned (on a personal note, ever since the Covid thing, this is my go-to.) Often this involves wanting to implement a certain strategy or have a certain chain of events unfold before even starting the game and seeing what your starting location looks like. But even at this difficulty level, there's a point quite early on, maybe halfway through the world congress's medieval era, where the player just starts to snowball and is producing 2 or 3 times the yields of the second-placed civ. In my current game (Maori/Terra/Religious), I've hit the turning point to start spamming 6-charge apostles and convert everyone to win the game. Unfortunately. at turn 126 I have 14 cities and am producing over 800 faith per turn and each of the other civs only have 6-8 cities in their empire, meaning I only need to convert 4 or 5 cities per civilization, and I see very little religious combat that I'll have to overcome. It would be much more epic to have to face carpets of apostles and need to convert dozens of cities, but that's the effect of playing at a low difficulty level.
Emperor: for when a proficient player wants to play a game where everything works out the way they planned, but compared to the previous entry they may have to delay some critical infrastructure to get some units out to deal with barbarian headaches. Without barbs, Emperor level lets you get those key improvements and second city out so fast that you've secured the game by your 3rd or 4th build; my opening build order on Emperor without barbs is often builder/settler. With barbs, I need a slinger and maybe a second warrior which can delay the second city and some happy/ecstatic yield bonuses for a dozen turns or so. Either way, looking at the great person recruitment history is a good indicator of when the game stopped being a game: Maybe the first page has a different civ recruiting each consecutive great person, but as you scroll down it's usually 7-10 consecutive great people that I recruited followed by one great person that another civ got (which is usually one of the worst GPs of that class as I boxed them out of the good ones) followed by another 7-10 great people that I got.
Immortal: for when a proficient player wants to play a game where there's some level of immersion and having to make adjustments to a few of the tactics they are implementing. We don't approach the game with a single strategy (Korea Seowon spam in every city to win science victory with minimal military necessary for DoW deterrent.) Instead there are several approaches (Korea Seowon spam for science victory, but also which city-state suzy bonuses to maximize, implementation of trade routes, timing-pushes for more free cities with pre-built infrastructure, faith accumulation and utilization, etc.) and at Immortal maybe one or two of these approaches may need to be forgone in place of a compensatory tactic, but the game is still going to play out the way you planned, just without being able to fully exploit the tactics you planned to use.
Deity: for a proficient player, if they want to stubbornly play the game using a certain set of strategies and maximize the effect of them(of which I am often guilty of) then they're going to have some frustrating times. But if you play adaptively to the situation, it's still quite the cakewalk. The time in which you start to run away from the AI is often quite later in the game, but you still hit a point where you can do whatever you want and be successful.
Having said all that and looking at your turn 100 map photo, I see that by that time you have 7 cities which is good; the benchmark to shoot for is 10 by turn 100 but the new rules make tall cities a more viable approach and you have to consider tile productivity, you're building walls in the right cities coupled with a well placed encampment to deal with the civ to the west, city and district placement are pretty good - most of your districts have adjacency bonuses (although I would have settled Pharsolas 1 tile east for a +5 holy site and +4 campus but that's fine.) In summary your understanding of the game mechanics is enough that yes, King is going to provide little to no resistance for you. The upside is that you're going to be able to surpass and dominate the AI very early on. The downside is that you'll reach the point where the game becomes boring because you have no real competition very early and approaching your chosen victory condition will be a monotonous, next-turn-clicking snoozefest, as well as seeing things like the AI hasn't even started generating one GP point per turn when you've already recruited several of that type, and finding yourself 2 or more eras ahead of the AI. My assessment is that you should be playing Immortal - at that level you'll have to play more reactively but still be able to outclass the AI quite early while seeing some of the resistance/efforts that you feel are lacking.