Just as an ideal nutritional supplementation program can be conceptualized and implemented, we can also conceptualize the ideal soil, then work toward implementing the conception. I'll describe what I want my soils to do and why, which I think is a good place to begin a conversation.
It's also important to recognize that there are 2 ways to look at growing. One is from the plant's perspective, the other from the growers perspective. A prime example of the difference is when the grower says, "I have a large number of plants and I'm not willing to dedicate the time it takes to water daily during those periods it might be required". I think that's a fair way to state it - no spin or aspersion. The plant doesn't mind at all if you have to water daily, in fact, it actually LIKES it. It means the soil is well aerated and the extra watering forces the exchange of soil gases for fresh air. I tend to always look at things from the plant's perspective, and believe that learning how to do that is the fastest route to green thumb status.
What I want my soils to do is, anchor the plant and provide a structure that ensures the plant has at least the opportunity to realize as much of its genetic potential as possible - this would be within the limits of other cultural factors that have the potential to limit. IOW - my container media should provide the best opportunity for a healthy root system that I can provide. That's reasonable, I think.
As growers, what defines our proficiency is our ability and willingness to identify and eliminate limiting factors to the greatest degree possible. Plants are already genetically programmed to be beautiful, all we need to do is learn how to avoid destroying their potential. That's worth thinking about.
Getting back on track - In order to ensure a healthy root system, we need to address at least a couple of things that are commonly limiting, so we can work toward excluding them. The big one is excessive water retention, especially in the form of water that 'perches' in the container, causing a significant fraction of the soil to remain soggy for too long. Tender roots are quickly killed (within hours) when deprived of air. Root function is also impaired by anaerobic conditions, so while parts of the soil are soggy you get both a cyclic death & regeneration of fine roots and impaired root function. Both of the former impact growth rate and vitality, and in a high % of cases, appearance. This is why I want to minimize or ideally eliminate perched water in any of plantings, but especially in those of plants that don't tolerate wet feet well (like cacti/succulents) and plants grown in shallow containers.
I suggest there is no need for the soil to 'feed the plant'. In fact, a very good case can be made that when you rely on soils to furnish important nutrients, the practice is more likely to be limiting than helpful. Providing all the nutrients essential to normal growth that plants normally take from the soil is monkey easy, which means the grower who directs focus on the soil's structure and shoulders the responsibility of providing for the plant's nutritional needs will likely have fewer problems and a much wider margin for grower error.
Let's see how close we are on what a soil should do, and then let's look at ways to best implement.