1. Happ is 4 years older than Saunders, and also is much more expensive, he's due to get 5 million in his next year, Saunders still has control (he's due to make a mere 2.9 million)
2. Happ is a pitcher. Saunders isn't.
3. Happ has been worth 2.3 WAR to the Jays his entire career in Toronto. Saunders has amassed that total last year, let alone 6 WAR in the past 3 years.
5. Contrary to your statement, Saunders has been an above average hitter the past three years (109 wRC+)
6. When the Jays traded Happ, he was going to be pushed off the rotation anyway, cause Stroman wasn't hurt then. The fact they got a cheap, above average outfielder for him was terrific.
EDIT: f*** JFaS already did it for me.