Mezzomix paid 200 BTC for a device from BFL that cannot earn 200 BTC.
You have agreed that this is not good.

Mezzomix is entitled to complain because the only thing that could have changed his fortune is if BFL delivered the Single before the difficulty went ballistic.
There is no current or future exchange rate into any alternate currency that can make Mezzomix's investment in BFL better than not investing in BFL when he did. Past exchange rates cannot change because they are in the past. So exchange rates are not relevant. We are not measuring just how screwed Mezzomix was by BFL, we are simply saying that he was better off not buying a BFL single back in June 2012. This is simple math. Obviously, the more valuable BTC become in USD, the more USD Mezzomix has lost. But we are not talking about losing USD, we are talking about losing BTC by spending BTC to buy a device to mine BTC.

All hope is not lost however. If difficulty ever stops rising for long enough, then Mezzomix will eventually earn his BTC back.
Maybe all the Avalons stop working due to shoddy manufacturing...