Earlier quoted context omitted.
The grandparent comment wasn't comparing arbitrary units, they were comparing the units of each country's currency denominations. The largest active legal tender in the US is worth $100 while the largest in India was worth $15 (now will be $30). I think it is a fair assumption that those numbers aren't arbitrary and that some thought went into choosing those denominations. That gives you insight into the economies of…
Largest banknote in UK is £50, largest in EU is €500. That does not imply a staggering difference in purchasing power between £ and €.
Things in the UK are a little more complicated with their multiple central banks, but the £100 note is still being printed and while uncommon, it is in circulation throughout the UK.