After the rather boring EPtS and TSS developments, we begin with more exciting things.
The charts for ST actually show a change over the course of the year.
I would probably say that I wouldn't be using ST3 if it weren't for Development Lab Scientists. Having 1 ST3 at global cooldown makes it worthwhile, imo. The addition of cruisers and carriers that allow you to slot it and the DOFF have turned it into a shield heal of choice. On a sci ship, you get 2 copies for the price of one, and open up a boff slot for something more offensively or debuff oriented.
Which probably lends reason to the dropoff of TSS3 and to the high level of TSS2 usage.