En el idioma inglés existe una diferencia entre T Shirt y undershirt, porque no soy yo solo el que piensa que son diferentes, a pesar de tus afirmaciones:
DO Wear an Undershirt, Not A T-Shirt
It is important to highlight that an undershirt is NOT the same as a t-shirt. Since it is meant for layering, an undershirt is generally thinner and more lightweight. Traditionally, undershirts are ribbed because a ribbed shirt can stretch more and is, therefore, more comfortable. So if you want to wear an undershirt, do not use a t-shirt because they are too big, too stiff and too thick to be comfortable undernjeath a dress shirt.
DON’T Show Your Undershirt
One of the worst style mistakes you can commit is to show your undershirt when you wear your shirt unbuttoned or when the lines show underneath your dress shirt. If you wear summer shirts with thin fabric, it is impossible not to see the undershirt, whereas winter or flannel shirts will reveal the lines of a well-constructed undershirt.
https://www.gentlemansgazette.com/un...t-to-wear-one/
Como señalas que nunca has leído sobre la recomendación de usar un cuello en "V" (o pico, como lo llamas), te ilustro con lo que encontré en una búsqueda rápida (aunque en el foro se ha discutido el tema):
Do Wear Deep-Cut V-Neck Undershirts
If you want to wear undershirts, always opt for deep-cut V-neck styles with flat seams, because one can see whether a man wears an undershirt underneath his dress shirt even if it is buttoned all the way, and he has a jacket on. If you take off your jacket, chances are you will show some rings on your upper arm unless the undershirt is extra thin, and close-fitting.
(...) The simple rule is this: The type of undershirt you should wear depends on the type of shirt you’re going to wear over it. Buttoned-up shirts should be worn with a crewneck that hides just beneath the points of your collar. V-neck sweaters, dress shirts worn unbuttoned with no tie and the like should be worn with a V-neck undershirt, like this classic one from Ralph Lauren. Do you prefer to wear a sport shirt with two buttons open? if so, then wear a slightly deeper V-neck shirt like this smooth 2xist offering. The idea is to match as closely as possible the height of the neckline with how much neck you plan on showing.
https://www.mensjournal.com/style/the-right-way-to-wear-an-undershirt-20130801/
(...) Replacing the crew neck with a V-neck is the obvious solution for men who want to wear a shirt with a few buttons left undone. The depth of the V-shape can vary, but most are cut so that you can wear at least one button (besides the collar button) of a typical dress shirt open without showing your undershirt.
https://www.artofmanliness.com/2013/...o-undershirts/
Podría seguir, pero como ves, no soy el único que considera que son la misma cosa, ni me acabo de inventar el uso del Vneck debajo de una camisa... Si, creo que hace falta leer.