That`s still really quick! I work as investor for a big Dutch bank, we see 3 to 4 years as a fast return of investment.
It is not ROI in the usually accepted meaning though, it's getting as much BTC for your USD with mining as you would by buying them outright.
Let's look at two scenarios: Albert and Bernard invest the same amount of USD today, Albert buys a mining contract, Bernard buys BTC.
- Scenario 1: Overnight, BTC value doubles. Albert is looking to get the same amount of BTC Bernard has in... 285 days. At the same time, Bernard can sell half his BTC, and buy the same mining contract as Albert and still have half his BTC already in pocket.
- Scenario 2: Overnight, BTC value halves. Bernard lost 50% in USD, but still has his BTC, and can bailout or hodl and wait for a bounce. Albert's mining contract does pay less than a trickle, "ROI" is measured in decades now, worst case being the contract does not pay its own electricity and is canceled.
The above scenarios are valid for any percentage variation, the doubling/halving is just for illustration.
Bernard (and buying) wins all the time at the current BTC price point.
At the moment mining contracts are an encouragement to the tech and the ecosystem, and they're an alternative to home mining as Ian pointed. But a profitable investment they are not, whichever way the BTC price will go.