So then you agree he should be glad the exchange rate increased, not that he bought a Jupiter?
first, OFCOURSE the exchange rate plays a huge part but that is just one of the moving pieces. purchased equipment, mined btc, sold btc, paid off all equipment and now can continue mining for profit. sounds perfect. could have bet his cash at a casino and have more or less money today. the point is, equipment is paid off and now climbing into the profits!
Yes when you buy a miner you are also investing in an predicted amount of BTC over a period of time instead of an exact amount you could invest in directly and sell at any point. Two different kinds of investment to choose from. So when measuring the success of an investment in a Jupiter you have two factors to consider. If you made less BTC than you could have purchased, then the miner was a poor investment. If you made more fiat than you spent on the miner then you made a good investment in BTC. People have a hard time accepting when they made a bad investment and choose to ignore the first and focus on the second. Yes we should be happy we made a fiat profit but don't fool yourself that it was because you invested in a Jupiter.
The same would be true with the opposite. If the exchange rate crashed but you made more BTC then the miner investment was good but the BTC investment was bad. People can gauge their success however they want but it is smart to be realistic and learn from the true cause and effect of your losses and gains.