Thinking like a lawyer first means being able to read like a lawyer. 121.436(a)(3) says, in part, only time spent as PIC IN operations under 91.1053 counts. 91.1053 is part of the fractional ownership rules. In other words, if you have not served as as a fractional program PIC, you cannot count hours spent as some other part 91 PIC towards being a part 121 PIC.

This situation is addressed in scenario 1 of the Kelley interpretation posted above and since it is an interpretation issued by the FAA lawyers, it carries legal weight. There's really no issue understanding WHAT the reg says, just an issue understanding WHY it says what it says.