IAH 73 is gonna see some weird dynamics in the next few years.

Prior to the new contract they vastly over-staffed IAH with 737 CA's because that's where the demand was. That is over and IAH has all the captains it needs for years. There will be occasional vacancies but expect very little seniority movement.

Holding a line as 73FO may take awhile too. But but, you say the current lineholder is only 9 months in (or whatever). Yes, that is true, but that person got in on the base nearly doubling in size. As it stagnates and the bottom 10% churns (and nobody can upgrade to captain) it's gonna take awhile to move above the g-line.