Still doesn’t make sense. If a tree cannot produce a fruit at all, there is no point in giving any gardening advice. If a tree under some conditions can produce a fruit, then again the concentration would be on these conditions and not on what the fruit is like.
The natural conclusion form this observation is what the Church teaches, that works done in the spirit of love (or charity) cooperate with grace and produce salvation. Since works is something man is at liberty to do or not do, it becomes important to Paul to urge them. Works is the gardening act, that cooperates with grace,— sun and soil. Fruit is salvation. Simple and biblical, no exegetical contortions needed.
At this point I may be getting a little lost in the analogy and what refers to what. :) I was just saying that Paul was saying to check the tree first to see if it is a fruit producer. If it is, then it will be profitable to work the soil to strengthen the tree and it will produce more and better fruit. If it is a bad tree, then everything stops until there is faith. No amount of work on a bad tree will turn it into a good tree.
Works is the gardening act, that cooperates with grace,— sun and soil. Fruit is salvation.
But not all trees are capable of producing fruit, no matter how hard you work them. Your contention appears to be that ALL trees are capable of bearing fruit if your work them hard enough. That just doesn't match what we know in nature. Some fruit trees are just bad trees and will never produce fruit. Works are only of any benefit to good trees.