So are science specialists ever worth it? Aside from having increased happiness by having less workers assigned in your city they really give limited benfit then. You'd get more benfit from having a tax collection specialist, having more in the treasury and being able to then assign a higher science slider because you'll be better able to afford it.
Actually, in
conquest, the scientist is usually more powerful than commerce turned into science.
For example, a working citizen on a road provides 1 commerce. with both a library and a university, that becomes 2 beakers (assuming 100% SCI)
And you can't run 100% SCI because those improvements costs upkeep.
On top of that, the they cost production shields, and turns to build.
In republic, that same citizen produces 2 commerce, and that will be turned into 4 beakers.
As you can see, using commerce and multiplier improvements. Is actually only really worth it in republic, compared to the 3 beaker scientist.
And then I'm only talking about the low corrupted core cities.
Of course, You'd rather have your core citizens work the land anyway because you also want them to produce food and production shields, but still. ..
In Vanilla and PTW you are correct, in those versions, I'd advice using tax collectors in your specialist farms to pay for the upkeep of core cities, allowing you to increase the SCI slider.