I think it's also important to separate logging advice for someone already flying for a 121 operation from that of a guy working his way through his ratings. Telling the OP that he shouldn't include over half of his flight time as PIC is bad advice at his stage. Once he's ready to move to the majors, with a few thousand hours of turbine, that couple of hundred hours in a C172 probably won't matter.
That's not what I said. I said if he worked at an aircarrier, he shouldn't log half his time as PIC
I did partake in logging dual and PIC when I was working my way up in the ratings. I don't take an issue with that. I fully understand the importance of getting the qualifications for meeting Part 135 mins, or an instrument or commercial or ATP rating. I even think you're foolish if you don't do it, for the exact reasons I stated in my post.
What I do take issue with is doing it as a designated SIC, at any level 121 operation.
Here is where there is a disconnect between an academic argument versus practical application. In a crewed airplane you are NEVER a sole manipulator of the controls. At least not in any crewed plane that I've flown (which in reality are few in number). The CA will taxi out, or if the SIC can taxi, the SIC will hand the airplane over to the CA for the brief. The Part 1 PIC will release the brakes. I guess from the interpretation you can log from when the brakes are released and you assume control of the aircraft to the point when you brief, to the point where the CA takes the aircraft back to turn off the runway. So a 2.0 flight might be logged as 1.0 PIC and 1.0 SIC then?
There is a GINORMOUS difference between logging PIC/dual recieved simultaneously and logging half your flight time as PIC if you are hired at a 121 operation and you are a designated SIC. I'm not sure if you've flown at a 121 operation, but you'd clearly see what I'm getting at.
When I did OT at the old shop and I'd get a right seat assignment, I was usually the senior pilot and a checkpilot. If I wasn't performing a linecheck, I was logging SIC.