You're looking at it from the wrong perspective. Mining brings in profit from day one and if it doesn't pan out you can just sell to get back what you paid. Investing it can either go up or down and if it does there's nothing to hedge against. Mining isn't as heavily linked to the price.
Where people are making the mistake is in looking only at the difficulty. The reality is that the difficulty has followed the price. Not really a surprise as more value makes it more attractive but it does mean the payouts have remained rather constant. Actually the price graph has led so the ROI has gotten a bit shorter over time. The difficulty has tripled the last 3 months but the value has double the last 3 weeks so something weird is happening in fact.
I can only give you the figures others have stated atm, ROI is usually in the region of 6 months at past rates.
It varies greatly with hardware used and how finely it's tuned but that is the general consensus. That's also without a value increase. If you happened to have mined last year and kept then the current rate would have halved your ROI period.
I wish I could give more info but I'd only be able to do that once I have everything up and running.
PS: And btw I'd be using my planned new Ryzen rig initially so if it doesn't work it wouldn't be a waste.