I think the biggest problem here is level of expectations. As I stated previously, 5E is very loose with rules, relying on DMs to make rulings, rather than trying to codify everything, as 3E and Pathfinder did. If you can't work within that frame, I have to wonder WHY are you trying to convert something from a game system that works for you to a system that obviously doesn't? There's nothing wrong with sticking to Pathfinder, or even 3E, and it's obvious 5E's rules light philosophy is going to cause you problems.
I started playing 1E 40 years ago next month. Within a year I had memorized all the saving throws by type, class, and level. I knew all AC combinations, loved using the Runka to disarm opponents, openly used the Melnibonean mythos in almost everything, and was trying to program more than my computer could handle in ASCII to speed up play. By the time 2E came out, I was starting to get irritated at all the rules changes. When I adapted 3.5 because someone asked me to run a pen and paper game for them, it was because all of my original materials for 1E was lost in a fire in a friend's apartment building. I purchased a used copy of Greyhawk and used 3.5 to imitate 1E play. However, I did not purchase the 10,000 tomes containing information such as: If you are standing 10 ft from a lava stream you take X damage, etc. And when D&D Next started up I was one of the first to argue for simpler play that would resolve faster.
There are two types of Character Development in D&D. There is RP development, which involves story telling, e.g. in the movie Braveheart the main character is Robert the Bruce (narrator) whose character actually develops through his experience of the unyielding unchanging paragon styled William Wallace. In 1E we did not spend all of our time flipping through environmental charts and tables to move across 10 leagues of map nor did we have to consult a dozen conditionals in 6 different books to obtain an outcome. So far, the truncation of the game in 5E has gone back toward a story telling style of resolution with simpler more concise dynamics during the most time consuming part of the play event. That is good because working people, who are likely a good portion of today's customers, want to be able to play during the few hours they can schedule play.
The other part of character development is the statistical skeleton which allows all the muscles to function in a dexterous manner. A part of that is setting up a system wherein a group of specific and exhaustive stats and structures can be put together for fast reference by people who have little time to test play materials for balance before they use them. The rules necessary to do that do not so far apparently exist in an official capacity. The DMG is insufficient - and intends to be, to that job. For one thing it references using other books. So, I have had to purchase additional books to do what should be in the DMG. (I just spent $70 last evening and should have the additional material within a couple days - living in the country those guaranteed delivery times aren't so guaranteed.

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There are places where the nebulous aids in making the story telling easier, and frankly inspires people to do research and at least read about the facets of nature they will include in their stories in order to enhance the suspension of disbelief. I didn't graduate high school because there was anything inherent in school which inspired me to learn, I graduated and went prepared to college because D&D drove me to learn the world around me so I could tell a better story. However, there are also places where creativity needs that framework from which to work. One can do epic paintings on the floor or ceiling when one has a patron and the time. However, for most realism requires strong definition of light and dark, of the negative space and the positive space, the blending of color, glazing, etc. There are rules for this which are prepared ahead of actually painting. I have seen some interesting art created by throwing paint upon a canvas, but nothing that I would create. The first fantasy story I ever read was Kim by Rudyard Kipling, the next was the Once and Future King, and then the Chanson de Roland. What makes the spontaneity of Shakespeare is what the actor brings to it in the moment of the execution - but the full form and structure is prepared before the curtain parts.
So, I am not looking for a 42" pile of books each of which must be referenced through each round of combat, watch through the night, and league of travel through the day. But I am looking for that framework which makes preparing the full and balanced preparation of game play take the least amount of time possible without having to break out a slide rule and spreadsheet in order to prepare the subatomic structure so I can prepare the atomic structure so I can alchemy together the ingredients so I can finalize the stats for the score of potential encounters into which the party might improv itself. I would rather start at least at the level of chemistry, rather than starting off by having to find the G-d Particle.

But I am attempting to read "Unusual Races Point Build 200" by John D. Batten. And I have ordered more materials from which I might get some answers.
As to the CR of monsters and players, they are the same. Just like all Wiccans are witches, but not all witches are Wiccans::Every playable race is also a monster, but not all monsters are a playable race.