Roman numerals were designed for a world where calculations were done on an abacus, and numerical systems merely recorded inputs and outputs.
In that world they are better than Arabic numerals, for the simple reason that your brain doesn't have to translate so hard between what you see, and what you record.
Also, this is how mental arithmetic is taught in modern elementary schools!
Lots of focus on "ten friends", and performing addition and subtraction by splitting into parts to make "ten" and then adding or subtracting the leftover:
The weird parts of Roman numerals is the lack of clear place value separation (no spacing, variable-length places I, II, VIII, etc), and using 5 V and 10 X so 2 different scales for place value, and the asymmetry of I,II,III,IV, V instead of the more consistent I,II,IIV,IV,V, and using relative position for sign instead of an explicit negative sign symbol.
In that world they are better than Arabic numerals, for the simple reason that your brain doesn't have to translate so hard between what you see, and what you record.