Both systems are broken. The British system is a bit more nominally consistent, but the names are poor; million and milliard are stupidly phonetically similar for what they are (generally we prefix those differences, probably because it's the ends of words that tend to get slurred, hence we have milli-meters and not meter-millis), and staggering the names out two chunks of 3 at a time doesn't really make much sense. It isn't very user-focused.
The American naming system uses roots more clearly and doesn't have the weird pointless bundling together of two groups of 3, but it has a bizarre off-by-one issue... and not the usual 0->1 or 1->0 issue, but a 1->2 issue. For consistency, the order ought to be "ones, millions, billions, trillions, quadrillions", so that the prefix on the digit counter indicates the number of factors of 1000 in question, from zero, one, bi=two, tri=three, etc. However, "thousands" get stuck in there wrecking the whole thing up, so where the names say you have 1 group of 1000, you in fact have two, and so on.
It's not an imperial vs. metric sort of thing, it's more an arguing which is the "real" temperature, Fahrenheit or Celsius, when in fact the answer is basically neither because the "real" temperature scale ought to have its 0 at absolute zero, like Kelvin [1] or the lesser-known Rankine [2], which is basically "Kelvin, except the degree is 1 degree Fahrenheit". These are both more "real" because now you can add and subtract temperatures meaningfully, which you can't do with either of Fahrenheit or Celsius. And likewise, neither number system is abstractly all that great. But then, that's part of why we have scientific notation.
What's wrong with the long scale? It's pretty consistent. Each name is the last times 1000, each new prefix is 1 000 000 times the previous one, and each -iliard is 1000 times -ilion with same prefix.
To put what I said another way, it emphasizes the wrong things. Nobody cares how many collections of 6 digits something has. 3 digits are what people care about. (Except where they care about 4, or actually vary the number of digit groupings they care about depending on where they appear, but then, this debate has no meaning to them anyhow.)
It's consistent, but it's consistent with something that doesn't match people's usage.
Both systems are roughly equally broken, so either side mocking the other for their number system is a display of parochialism above and beyond the usual levels one would see.
This "off by one" issue, combined with the problem of words related to latin "mille" for thousand in many languages, is why in money people often use K for units of "1,000", MM for units of "1,000,000", and B or sometimes BB for units of "1,000,000" (BB has no meaning as far as I'm aware, people just copy the style of MM).
Unfortunately it is likely too late to really adopt the metric system for financial transactions. But the K has crept in for thousands.
> million and milliard are stupidly phonetically similar
Hi. I live in Poland. We use "milion" and "miliard" which sound exactly as you would say them in english and somehow I never met anyone who would have problems distinguishing one from the other, phonetically. Soo... maybe not that stupid after all?
No offense meant but it's usually shown as an example of the "Americans can't count" stereotype: 1,000,000,000 is a thousand millions.