Discontinue the esoteric technical jargon of "challenge ratings".
Instead use "levels" for both monsters and player characters, whose meaning is obvious.
In principle, it should be easy to create a monster of a specific level on the fly, using a chart. A DM can customize it with normal player character rules, plus a hit point boost and heavy damage for several rounds.
Establish a reliable sense of what level a monster needs to be for "medium difficulty" for the players to encounter.
Relatedly, establish how many lower level monsters approximate a certain level monster.
Xanathars has some useful approaches but I am unsure if its numbers pass the test of time. There seems to be different schools of thought among D&D commentators.
Making encounter building simple to understand and do, helps make DMing a joy.