What we call cornflour in British English, and cornstarch in US English, is flour heavily processed to remove everything except starch, giving a flavourless thickener.
If you use wheat flour you will change the flavour and also add a slight graininess as the flour grains don't completely homogenise.
In Italy we just add to the pan some of the water in which the pasta was cooked; this is rich in starch due to the cooking process. This works with other recipes as well, for example gricia or aglio olio & peperoncino. I guess that adding flour would produce a texture more similar to gravy and that's not what we're going for in traditional Italian cooking.
This is addressed in the paper, there isn't enough starch in the water for it to reach the ideal proportion unless you "risotto" the pasta (I don't think there's "risottare" in English sorry).
Adding corn/rice starch is advised by some Italian chefs too cause it's just a lot easier to get a reliable result (see the videos on Italia Squisita by Monosilio).
You can eyeball it with pasta water, it's just harder.
That's one thing I never quite understood on the "Italian" way to cook pasta (basically "use a bucket of water"). Using just the bare minimum ("risotto" as You call it) is in my opinion way more efficient and opens up a lot of interesting options (i.e. using the residue for a sauce). There's an extra step (the need to stir occasionally), but it can also remove a step (straining may be superfluous if the residue is used for a sauce base).
E.g. continuously stirring the pasta while you could be doing something is a waste of time where you could be doing something else, so less "efficient".
Turning off the heating and letting the water cook covered uses very little energy but takes more real time so also less "efficient" in a way.
More active stirring also tends to break up the pasta, so depending on what kind you use you may end up with a different outcome (works great for pasta e ceci or pasta e fagioli! Wouldn't want it for spaghettini)
Mostly, I think the traditional way seems unnecessary because modern pasta is a lot stronger than it used to be. I you try to make a one pot pasta with low quality pasta (low protein) you may end up with glue (source: am Italian, live in country which produces shitty pasta).
Yeah, lot of cooking is up to personal preference. In my case efficient here means using less water/energy. Optionally it can also be using less time, but that depends on what the end result is supposed to be.
As for the stirring, I'd say "it depends". Personally, I prefer to use fresh egg pasta. It cooks in maybe 2-3min and does require maybe 1min of stirring (maybe 20-30s in the beginning and end and perhaps one or two quick checks in between). I'm fairly sure I'd stir it somewhat of I used more water and I'd definitely need to strain it, so there the amount of time / effort is at worst the same, at best slightly in favor of using "risotto" method.
When it comes to dry pasta, I guess it depends on volume. If You're cooking a batch for 10, the traditional method probably makes sense. Otherwise, I pay attention anyway to how much the pasta sticks and clumps together.
the traditional way to cook cacio e pepe and the other recipes I mentioned in my GP comment is to move the pasta from the pot to the pan, then add some of the water from the pot to the pan so you have the "risottare" phase (most people in Italy would call that mantecare, at least in central Italy). I appreciate that adding something like corn starch would make it thicker, but also different people may have a different understanding of the concept of "creamy".
Risottare is cooking the pasta in little water (or other liquid) so all the starch stays in the pan/pot, adding water or sauce as needed. This is the part you do with broth when cooking rice for risotto.
Mantecare is when you mix the pre-cooked pasta with condiment in a pan, possibly adding some pasta water. This is the part you do with butter and parmigiano when making risotto ("mantecare" comes from "manteca", spanish for cream/butter).
You can do one, none, or both for a given dish, and get different outcomes :)
OK I get what you mean, I've seen risottare before used as a synonym to mantecare (I think it was some Italia Squisita video) but it makes sense that it's actually what you describe i.e. cooking pasta like a risotto, hence risottare. Thanks for the link
One small clarification: rather than cooking your pasta in less water, the paper actually describes boiling down the pasta water to further concentrate it ("risottata") by reducing its weight by 3x (presumably shifting your starch concentration from 0.5% to 1.5%).
That said, as you mention, it's just a lot easier to get the consistency right by adding your own starch in measured proportions.
This seems wrong. My Caccio recipe begins with specifying the exact volume of water, derived from some experiments I performed when my son first asked me to make the dish. I also performed experiments to get the exact time the pasta should be boiled (it has to be removed to the skillet prior to being done so you either need a time machine or prior experience to know the time, which varies with altitude). Nowhere does this dish call for "yeah just fill the pot and throw in some salt". The salt also needs to be carefully controlled because the water ends up in the dish and the cheese is salty.