OP's right, but designing an UI
is hard.
Designing a user-interface from nothing is difficult, but in 2018 any computer game developer can look at a plethora of similar games from the past for guidance, even if only as a cautionary example for how
not to design an interface. For CRPGs, specifically, there have been two pioneering graphical user-interfaces.
First, Dungeon Master from 1987, which created the "paper doll" inventory screen and for its main interface ringed the central first-person view with controls and info relating to each party member, the party members in relation to each other (and individual party member facing!), the magic system for spellcasting, weapons/items held by each character for immediate use, and directional movement --- all contained on one screen!
Second, Morrowind from 2002, which had basic information at the bottom of its first-person (or optionally behind-the-shoulder) view but where pressing the right mouse button would instantly pause the game and bring up four windowed menu screens, which could be resized and moved around as desired. The image below is from Mobygames, and the windows have been moved and resized from their defaults, but it demonstrates the separate menus for inventory, magic, the map, and character statistics.
In the wake of the example set by Dungeon Master, CRPG graphical user interfaces experienced a general incline for an extended period of time, but eventually they began a retrogression, prompted in part by consolization (compare Oblivion to its predecessor, Morrowind, for example) but continued for reasons that are hard to fathom (Skyrim's UI is almost a joke, as though Todd Howard wanted to see how horrible a UI could be while still being played by console-users who, unlike computer-users, had no means of modding it).
Of course, any user interface should be tailored to the needs of its particular game. For a CRPG, this means first designing a user interface suited either for turn-based or for real-time and either for a single-character or for a party, and continuing from there based on game mechanics.