I think the issues isn't about having one good year, it's the position the opt-out leave the club in. If they sign Holland to a 2 year deal worth $8 Million for the 1st year (plus incentives, perhaps up to an extra $2 million), and a 2nd year worth $10 million, with a player opt-out, it could totally hamstring the organization. If Holland is great, he gets to walk and sign a better deal; if he's terrible, he has the insurance of an extra year at a high salary. There is no risk for him.
For the Jays, though, they are risking signing a player coming off a serious injury that could be a total waste of however many millions it takes to sign him (I'm guessing somewhere between $8-10 million). Signing Holland to a 2 year deal mitigates that risk (especially if it's a team option) because if he is great, you have him locked up for another year at a reasonable price. The player opt out negates that benefit to the team, so they are now taking on all the risk of Holland either getting injured again, or being ineffective, without much reward should he go back to being an elite reliever.
Now, I'd love for the Jays to sign Holland, perhaps even if the contract contains an opt-out, but I understand the reluctance of teams giving those types of deals out. It's basically an insurance policy for the players; if they suck, or get injured, they have a guaranteed salary, and if they perform to the expectations of the contract (or even better it), they can opt out and get a better deal. It's a no-win situation for the team.