The whole point of the galant style "revolution" was a very heavy focus on cadences. The Vienna classic stuff that comes after is even more cadence-focused. I'd say that's kind of the main stylistic point, that it's cadence-oriented. So, if you're using secondary dominant chords, they need to be in the context of a cadence for it to be in that style. So, sure, you can do T (DD) D T or more typically T (DD7/b5) D T, but that stuff needs to go in the context of a cadence and cadences are what control structure. That's why it seems "older" to do the thing you're doing, which is vary the harmonies outside of the main cadences.
Notably the biggest exception to this is modulations, which can happen outside of cadences through development sections (sequencing and division of motifs.) Even so, you'd be hard pressed to find modulations that don't include a proper cadence.