The comparison is faulty because AM is a company and the other alternatives are hardware.
Why is that relevant, you ask? Well, AM will (hopefully) continuously renew itself and its strategy in order to keep earnings high, whereas the hardware simply gets outdated and earns progressively less and less as time goes along. So: buying hardware may earn you more in the short term, shares in AM may earn you more in the long term.
Comparison is NOT faulty. It is a comparison of "investment" (whether in hardware or a company) and "return" (whether mined bitcoins or dividends paid out as bitcoins). I think most people will agree that the value of hardware (GPU or ASICs) will generally depreciate over time, so that is a "known." The big unknown is AM, which as you point out is a company. We hope they will continuously renew itself, but anything can happen.
It is faulty. Usually "return" is calculated as the appreciation in share price + dividends. If we make the assumption that the share price stays the same indefinitely, you will certainly realise a positive return whenever you choose to sell your shares. Obviously we would like to see the share price appreciate as well.
The rest of the investment examples are correct and you fix your GH/BTC rate when you purchase. With AM, your GH/BTC investment will increase overtime as Friedcat expands his mining effort and switch to 2nd gen ASICS etc. In the long term, this is where you want to be!