The TCI is broken. Some of my favorite examples that reaffirm this are similar types of airports with different levels. In this case, let's look at some the some core 30 towers.
In the past 12 months, FLL has worked 12.5% more planes than IAD and they did it with half as many runways. The vast majority of the traffic at both airports is IFR commercial intinerants. The major difference is IAD gets 25% extra for being a class B compared to FLL's 10% for class C, and IAD also gets 10% for having a converging runway.
For the same 12 months, IAH worked 1.8% more planes than MCO. Both class B, but IAH gets the converging runway multiplier and that somehow gives them enough to be an 11 vs MCO as a 9. I think the fact IAH and IAD are hubs also probably helps their count over MCO and FLL since the traffic during their busiest hours is condensed by departure/arrival pushes.
One more thing I find wild is that MYR is a 9. I think their TCI is heavily carried by the fact that from about April to August, they have these 2 helicopters that just run land on the SE side of the runway, takeoff and fly a sightseeing tour up NE up the beach a few miles, come right back, pick up more passengers, and do it again. All day, everyday in the summer. And they count them as air taxis. Their air taxi op goes from like 2k in January to 18k in July. The crazy thing is I listened to a little LiveAtc and I didn't hear them talk to the helis at all. I think they just have an LOA where they're probably monitoring the freq. Meanwhile they get a tower and a tracon count for it. Insane. Meanwhile RSW is also a single runway Class C and they ran twice as many IFR itinerants as MYR in the past year (almost triple the amount of air carriers) but they are an 8.