Point is though, I think it's not too much up or down in value from its earlier form.
In the pre-patch vanilla game, not counting specialist slots, a Public School adds +0.75 beakers per population (the base is 1.5/pop for city and Library, and this adds +50%), although this goes up a bit if there are any non-population sources of beakers (like an Academy or a Scientist specialist); not much, though, since these will be far outnumbered by the population as a whole.
Post-patch, a PS adds 1 beaker per population point, but this gets +50% for the University (which you WILL have), +50% for an Observatory (which you might have), and then +100% for a Research Lab towards the end. Ignore the RL for the moment; you're still looking at 1.5-2 beakers per population. Let's assume you DO have an Observatory, since I want to examine the worst case scenario for making a science-oriented city.
So you're looking at a difference of 1.25 beakers per pop. For a size 16 city (fairly normal for core cities in the Industrial era), that's 20 beakers per turn more than the old version gave. At size 20 (which you'll get to by the Modern) it's 25 beakers. And so on. Once you get the Research Lab the discrepancy just gets HUGE, but again, we're talking about before that.
A difference of one specialist slot isn't even close to enough to balance that sort of difference. And if you look at the math you quoted, you'd see that the vast majority of the 5-15 estimate hinged on the creation of a Great Scientist... except that great people just don't work that way. If you build a Public School in every city (which you SHOULD, currently), and fill a scientist slot on each, it's not like you'll get a GS spawn in each of them; only the schools in your core cities (those with +science Wonders or other specialist-filled buildings) would ever have a chance of spawning one, and only then at the expense of OTHER great people types. (Make a Great Scientist, and the threshold needed to get a Great Engineer goes up.) And a specialist doesn't just cost 2 food (or 1, with the right policy). There's also the opportunity cost, the amount the tile they could have worked would have produced. So that citizen you allocated as a scientist for a handful of beakers could have been used to give the city food, production, and gold from that grassland tile nearby.
That's why you can't count specialist slots on buildings as a pure gain to their output; in most cases, it's not even a GOOD idea to fill your slots. An Engineer, for instance, would be better served working a Mine tile (which probably generates more hammers and usually also adds some gold)... unless you have no mines available or really, really want a Great Engineer. So you could put ten Engineer slots on a Factory, and it wouldn't make it any more powerful in practice unless someone wanted to go out of their way and make a Great Engineer in spite of the lowered output.
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It's your mod, do whatever you want, of course. But there's a reason that in my own mod I changed the PS back to its old version, and then tweaked from there. In practice, it's just far stronger than it used to be without this sort of change,