Perfectly said! Bravo.This is a great question. Let's restrict the answer to products that lather.
The continuum goes from lather to cream to croap to soap. Croap is combination of the words cream and soap.
There are few lathers as they are already lathered. It takes a lot for each shave. Cream is soft like butter. In general, it's easy to scoop out a bit with the tip of a spoon or a popsicle stick. Because they often contain glycerin and other products the concentration of actual soap is less. In general, they are more suitable for people who are experienced shavers. Beyond soap, there is triple milled soap, which is very hard and lasts a long time.
You are trying to balance two characteristics. Slickness and cushion. Slickness refers to how easily the blade slides across the face, but really it's how close it allows the blade to get to the face. We are talking thousandths of an inch here. Cushion holds the blade slightly away from the skin. You won't get quite as close, so there is less chance of irritation with good technique.
In general, the harder a shaving product is, the fewer grams you will use per pass. Soaps generally last far longer than you want them to. For instance, I get about 166 two-pass shaves out of a 50 gram puck of Williams. I've seen people say they only get 60. No matter, it's still a lot.
Practically speaking, you need to make a choice to start someplace. The best place to start is the product you have and learn to use it to its potential. This probably means about 100 shaves with the product. You will learn a method and the amount of moisture to use to vary the slickness and cushion.
In my opinion, switching soaps to get better performance is an endless game that doesn't work. It leads to thinking the quality of the shave is more dependent on the product than the shaver. It also leads to a drawer full of soaps you never use.
The best teacher is shaving, even if you need to just practice lathering a few times a day without actually shaving. In the end, your opinion will be the one that counts.