Wouldn't feed method have a large part to play in "depleted soil"? If I'm dumping bottled nutes into the soil then whatever nutrient composition the soil has takes a backdoor to readily chelated liquid fertilizers right? In other words, the plant is relying on manual feeding rather than organic matter being broken down into soluble ions that the plant can use. Certainly these organic reactions are important in having a readily available food source for the plant but it would seem that if you're supplying it with readily available food whatever food the depleted soil is able to produce would be secondary to the plant.
Also, if I'm reusing potting soil that I've grown in before and am using bottled nutrients would not whatever residual salts that are left in the soil be enough to recharge the soil with readily available ions? I know that some will veg with only water for about a month using the natural nutrients that the soil provides but if you're using liquid fertilizer from the start then, again, you're providing the breast milk not the mommy.
BTW I need some tips on growing heirloom tomatoes. Those bastards are finicky as all hell.
Soil is not inert.
If you are using soil, it has what is called cation exchange capacity (CEC). This allows positively charge ions (many nutrients are taken up by the plant as positively charged ions, like potassium, calcium, magnesium, iron, manganese, copper, zinc, and others). to be held by the soil, sort of in reserve. It is released slowly to the plants. It doesn't easily wash out.
You also end up with different nutrients reacting with each other, forming compounds of low solubility, which also don't easily wash out of soil. These can become available to plants at unknown rates, so when you are feeding on a regular schedule, you won't know how much is also being released by these leftover compounds.
Heirlooms: They're like regular tomatoes, only moreso.
The main issue I have with heirlooms, is that many are crack addicts. The only way I've been able to stop varieties like Black Krim from cracking is to water every morning. If the soil dries and then is suddenly wet again, the plant will suck in water in over-abundance, and fruits swell and crack.
Then, tons of calcium. I've never seen calcium lockout with these bastards.