If he's coming off two big years, yes, he will definitely get more than $81M guaranteed.
I don't think it's that clear. If this year's market is a consequence of the new CBA, I don't see the 2019-20 market being much more lucrative. And as I mentioned a couple days ago, the free agent market that year is loaded. At best, he's going to be the 3rd most desirable pitcher on the market (behind Sale and Bumgarner, who will each be 3 years younger than him). If Gerrit Cole re-establishes himself as a TOR pitcher over the next two years, he'll be 4 years younger and more desirable. And Gray, Odorizzi, Pineda, Porcello, Wood, Hamels, and McHugh could be nice targets who might be available for less.
I guess it depends on your definition of "big" years. If he's a Cy Young type pitcher the next two years (and 2/3 of Bumgarner, Sale, and Cole lose value), then maybe it makes sense. But if his big years are more like #2/fringe ace years (4-5 WAR), I think he'd have trouble finding more than 4/$81 at that point.