Based on actual results this year - he's been a very solid pitcher for the Blue Jays.
However, by all indications, he's been very lucky to achieve those results this year. All the advanced metrics suggest it's not sustainable, which is why no one was overly surprised by his recent struggles. Am I concerned with what he'll be moving forward? Obviously I am. The good news is pitchers are volatile from year to year and his Stuff + is still good. With a few tweaks this offseason, there's a possibility he'll be more effective next year. There's also a possibility his struggles will continue and he won't be as lucky next year. Time will tell.