alt Hacker NewsThe logic isn't flawed. If you are a European investor, then you care about the returns in your currency, and the fact is your pile of money only grew by 4%.
Inversely, as a US investor, if you invested 100€ in the eurostoxx 50, your pile of money would have grown to about $140 (20% index growth, 15% dollar debasement). It absolutely makes a difference, that's $20 more in your pocket compared to the index.
Your comparison with temperatures is wrong. Celsius and Fahrenheit are fixed units, whereas the value of currencies fluctuate.
It is flawed because it's conflating two different independent variables. It's also looking for a specific weak point where there is none, more as if it is trying to state a narrative.
If you want to talk about EURUSD then just state it.