Drak, that's nuts because it's exactly what I do as well. I exclusively play Mystery Heros and occasionally jump into competitive games. The great majority of my play time is in Mystery though... it's great for learning all heros and getting comfortable with them, but it also gives you a better understanding of the enemy you're fighting in comp. It's almost necessary to stay sharp as they keep changing heros around, re-balancing them constantly.
Bastion is def. OP in Mystery Heros mode, but I totally get wanting to jump into turret and blast away. He is more difficult to play now, but he can tear shit up in the right position. I struggle with staying alive when I'm bastion in comp. as the enemy almost immediately has a good counter for him and pushes hard to get through to you. Only other heros I struggle with now are Winston and Genji. I can occassionaly make Winston work in Arcade, but if I try to play him in comp I get destroyed. Genji just feels week to me when he's not ulting. I get that he has great mobility, but I can't see to use it very well.
Anyways, you should see about jumping on a NA server sometime and teaming up for MH or QP. I'm usually playing during the day for an hour or so, sometimes at night as well. My battle tag is: LaNdoColt451978
I took a long break from the game and haven't touched comp for about a year, but now that I'm playing again I'll be jumping in next season which starts tomorrow or today I believe.