I can’t argue it. He is a nice #4 starter. If you expect ace then of course you will be disappointed
That said; if they pull Hamels opt and Darvish gets 100% then he is your #5 and is a bit pricy as one. But with injury and decline ahead it would be stupid to weaken yourself at a vital area to strengthen another.
Except $10 mil is the price of a #5 on the open market and you can see that borne out over the last few years. It's also why a lot of teams don't sign #5 pitchers and rather develop them from their system. Q's number over the years do not paint him a a #4 though, in fact in his best years he Hamels and Lester have stats there are nearly identical. I'm not saying there's not a difference because there is, Hamels and Lester have that extra thing where they know when to throw the big pitch in the big moments and Quintana struggles with that but in all the major stats K/9, BB/9, ERA, FIP, WHIP these guys compare to each other. To me that makes him a 2/3 type when he's on. Quintana was better last year with the Cubs than people given him credit for and he's been better most of the year this year than he's being credited for. He was bad in May and July which is why at the end of the day this year will most likely be an outlier in his career as he's too young for it to be considered inevitable decline. Given career stats and a presumption of regression to the mean and health a rotation of Lester, Darvish, Hamels, Hendricks and Quintana has to be looked at as about as strong a 5 man as you can reasonably put together. Lacking the highs of a Verlander it might not be on par with what Houston threw out in 2018, but close.