The problem with old units...
"The yard was a stride. A league how far you could march your soldiers in an hour. A furlong was how long you could have your ox plough before it needed a rest (so why not turn around), a rod was the width of the plough's effect and so the acre was how much you could plough in a day (being X rods by one furlong, and the most efficient shape to give to your peasant to farm)."
The problem with old units is that they're barely better than nothing. They varied _massively_ between people "measuring" them, and over time too.
E.g., the acre was already getting obsolete around 800 AD, when someone figured out how to use a _horse_ to plough. It worked out entirely differently than the ox-driven plough that the old acre was based on. So although it would be centuries before most peasants could afford horses, already a gradually increasing number of people were stuck with a unit which, used exactly how the original logic behind it went, ended up with decimals. "How much you can plough in a day" was no longer 1 acre, and fields divided into 1 acre plots became more of a pain in the arse than something anywhere near useful. Which is one of the many reasons why they gave up on that system.
Second, soil type? Plough type? And are/were all oxen created that identical to each other? Etc.
Stride... Whose stride? The average person's hight rose gradually over time, partially because kids get better food. But even at any given time, two persons of different height would "measure" a very different "1 yard". Heck even the same person at two different times, you can bet on a bit of variation.
Which is why even the imperial system gave up on those vague definitions and came up with standardized yards, inches, gallons, tonnes, etc. They're just as artificial definitions as the French metre or kilogram. But you need some standardized pound, inch and foot to do any kind of trade or engineering work. If you rely on noting the sizes in strides, the tolerance is too bloody huge for any practical use.
Even very early, well, let's just say you have words like yardstick -- and the metaphorical expression that something is the yardstick for some domain -- because they really used that kind of crude standardizations. They didn't actually measure in strides, they had a stick cut to the value they had defined as 1 yard. (And similar "standards" for everything else. E.g., for liquid units they had containers of standardized capacities.)
Basically, no, the old units, as they originated, weren't fine even back then. (Otherwise, see above, they wouldn't have needed yardsticks.) And then got standardized to some arbitrary, but uniform value. It doesn't matter if it's one stride, it matters that 1 yard is 1 standardized yard. Whether or not it fits your stride (most likely not), is irrelevant.
And at that point, if you're using some arbitrary standardized unit anyway, you might as well pick one which also gets conversions right.