On the one hand, I feel like this comports with what I'm seeing; that the new 2.5 GHz antennas are not popping up as quickly as I would have thought. On the other hand, a lot of the gear in the big cities is on rooftops, rather than towers. While some rooftops are contracted to American Tower or Crown Castle, I have to imagine a decent number of them cut out the middle man entirely and work directly with the carriers. My home site on Sprint appears to have the new T-Mobile antenna, and it's on a high-rise. The other site I've seen around here with the new 2.5 GHz antenna is owned by Crown Castle.
That's pretty typical outside of the cities, as far as I have seen. Pre-existing sites that had Band 2 gear got converted to LTE and some of them (not all) got Band 12 added. They've added Band 4 when capacity needs demand it, but that's about it.