I made a fairly concise point, but you're right about one thing
>we all do this sometimes
Because you most certainly just did
>As for your specific concerns: the easy pattern is that the letter for a group of five literally looks like half of the letter for a group of ten.
That's not the issue with the "easily repeatable pattern". The issue is this:
>V = X/2, L = C/2, D = ↀ/2, ↁ = ↂ/2, etc.
Do you see that "etc" you post? That's because, to represent 10^n, you need to know 2*n + 1 characters.
This is an obvious downfall that Hindu-Arabic numerals obviously do not have. Even if you ignore the shorthand (which would be foolish, parsing 5-9 characters in a row can take a serious moment of focus), you still need to know an unbounded amount of characters to represent the integers alone, and let's not even discuss the obvious fallacy of fractions etc..
Also,
>Objectively, the Roman system is easier to teach up to a basic level
Even this is an unfounded statement. Make an argument. Prove it. Objectivity of teachability can't possibly be something you just throw out casually in an argument, let alone an argument where you told someone they were biased and ignorant for, as far as I can tell, no reason at all.