You can do long division just fine on a counting board, though it is unclear if people had developed something like the modern elementary school division algorithm 2000+ years ago.
We don’t really know much about people’s calculation algorithms, because they were an oral tradition not written down, and only a very small number of counting boards (e.g. made of marble) survived; others were presumably made of leather, wood, cloth, lines scratched in the dirt, ....
Japanese soroban experts handily beat westerners at doing division, in both speed and accuracy. There is no reason to believe that calculation experts of the ancient world would not have been comparably competent.
Counting boards / the abacus are about as good as you get for calculating methods until mechanical calculators and logarithmic slide rules. So it's not really fair to say the Romans had a disadvantage here when no one had anything better. (Granted, the wire abacus was faster than counting boards / jetons).
An (analog) slide rule is a whole lot faster than doing digital arithmetic. But it’s approximate, yielding about 3 digits of precision, or maybe 4 digits on a large slide rule.
With an abacus or with written numbers, you can get 10 digits of precision (or 50) if you are willing to put the work in.
You can iterate slide rule calculations to get more precision, too... You're not restricted to the width of your abacus nor the number of sigfigs you can get in a single slide rule calc..
I think you just made my point :-)
Have fun doing long division that way.