Fourth pic over from left is the most dangerous code allowed installation. No safeties will shut the furnace off if the flue gets plugged or blocked above where the water heater "Y"s into the flue. The furnace will continue to run and the flue gases will enter the through the draft hood on the water heater if flue gets blocked.
I agree. Wye is in horizontal position too. It does have a flue liner which helps a little bit but please understand that where i work moves so much equipment and we have four crews doing two jobs a day! (fulls, halves, whatever) The majority turn out nice and clean. If there are any issues we take care of them right away. I like to think my installs come out pretty good in the allotted time that i do them. I spent most of my career in a shop that didnt care if it took three days to do do a full system but that company is about out of business. Thanks for the compliment