It's not more precise, it becomes inaccurate.
A man says he's 6'6". Sure. If he's anywhere between 6'5½" and 6'6½", that's true.
You say he's 198.12cm tall. The range of this being true is now thinner than a needle. It has gone far beyond what anyone actually measures. In over 99% of cases, it's not true, and if it is, it won't be for long, because the human body isn't nearly that consistent from breath to breath.
The conversion with spurious false precision has made the number go from true to not true.
The man is six foot six, yes, true. The man is 198.12cm - no he isn't.
While I normally don't give the Brits much credit, gotta say NI is not being held in the UK against its collective will. Your imagined cruel English oppressor holding on to land by force, opposing the will of the local population, is out of date in the 21st century.
Almost all Brit politicians would love to be the PM at the time of Irish unification.
Since 1998, the NI Secretary is obliged by treaty to carry out a referendum for unification as soon as polling indicates there's a reasonable chance it would get a yes majority.
It just hasn't happened yet. It probably will, within a few decades.