As Eleshar pointed out in a comment, the Roman numeral system is more flexible than many sources let you believe.
However, the rigid system usually taught in schools actually does have a kind of positional notation.
For example, 43 is XLIII, or 40+3 is XL+III.
The decimal in the first position is fully expressed before moving to the next one.
For example, 1994 = 1000+900+90+4 = M+CM+XC+IV = MCMXCIV.
Admittedly, this is not fully positional notation since a varying number of symbols (from zero to four) is used to express each decimal.
However, after playing with Roman numerals for a while you will learn to recognize quickly where the decimal changes.
In reality the Romans used many variants, and not all of them had this positional property.
The Roman words for numbers were no less sophisticated than the modern English ones.
Actually quite the opposite: Latin had (and still has!) four kinds of numerals for different uses whereas English has two or three.
For number one, the words are unus, primus, semel, and singuli.
In English these are "one", "first", "once" and "one at a time".
(Not all numbers have the third version in English; you have to say "ten times".)
Observe also that the Roman numeral words do follow the decimal system.
Roman oral numerals were hardly "arcane numerology" — or if they were, so are the English ones.
The Roman symbols for numbers were clumsier than our modern ones, but they have little to do with how the numbers were pronounced.
It is worth observing that the Romans did not have separate symbols for numbers like we do, but they used letters from their alphabet.
(For large numbers they used some additional symbols, but let me not digress.)
Had they had separate symbols, I believe they would have come up with a simpler system.