This statement is wrong.  It's actually the opposite of the truth.

Cost is a result of perceived value at the time.  Therefore the cost of something will change in time along with it's perceived value.  This is accentuated by inflation over time, which is similar to a moving BTC rate.  So I guess you probably think anything purchased 300 years ago is an amazing investment because you got back so much more USD than was invested.  You can turn a blind eye to the fact that it's possible your purchasing power didn't change at all so in fact you gained nothing.

I see your issue though.  You are trying to evaluate something incorrectly based on your personal experience.  You say, I paid this amount, so that is my investment cost.  The problem you are having is that you are paying an investment cost determined by the USD/BTC exchange rate in USD and trying to pretend your investment cost is solely in BTC (so while you argue that your investment cost cannot change, you are in fact going back in time and changing your investment cost with each tick of the USD/BTC exchange rate).  For people used to staring at their brokerage account in only 1 currency and seeing the cost/return, this might make sense.  For someone with experience dealing in multiple currencies, it appears that you obviously don't understand what you're doing.

I hope that makes sense, I admittedly didn't explain it well but tried my best to do so in a way that might finally click for you.  If not, I'm sorry for your future investment losses.

EDIT:  Why not list these securities in a 3rd party value that is neither BTC or USD to give another non-bias opinion?  It seems that might be a better way to do it since people don't seem to grasp this whole multiple currencies evaluation thing.  I know why of course, it wouldn't be a good troll and the OP's intent was not to provide any useful data, but to simply bash the market he failed miserably trying to control and will ultimately imprison him.