Is everything that David, the Merciful, did for good?

The troops have a choice and he doesn't want to prevent them from being able to raid a city whenever they want (or influence the weights in each of them). What is not true is the spirit of a lion and a cat, who apparently have no choice and it's convenient for him to intervene through them (and even if they do have a choice, it's less important to preserve their choice).

And what about a confession about being saved from disease or evil animals?

The questioner assumes that not everything is for the best. Or, more precisely, he assumes that he knows what is good and what is not good.
If he understood that everything is for the best, he would not ask.

The problem is only a problem for those who think that every scoundrel who fell from the net of the Lord was thrown, and every spider that ate a fly was stung, and every person who picked his finger off the bottom was stung. And this is truly a strange thought, and those who follow in the footsteps of the Maimonides do not think it.
But even though there is private supervision, the world still behaves as it is customary, and lions devour their cubs and strangle their lionesses, and the Lord does not intervene and allows them to do as they please (why? Here your well-known method is enlisted in our favor, according to which the merciful and nerdy God is very interested in the laws of nature and apparently there are no more successful laws that would advance his hidden goals with less collateral damage), and when he does intervene rarely, then it is appropriate to thank him.

When there is an extraordinary rescue, then if you believe in private providence, you can attribute the rescue to the extraordinary intervention of God. In particular, Rabbi Akiva, who, according to the virtue of man, is so great that the degree of assistance that God extends to him is such that the feet of his followers will be protected, and therefore, when an extraordinary incident occurred with him (he probably was not negligent in putting out a candle that went out in a common wind, but rather in a wind that was not common, and a cat does not usually attack chickens, and a lion does not come to a place where it lives. These are things that raise an eyebrow), attributed it to the hand of Providence. In general, it is always possible that rescue is also part of the laws of nature, but if you believe in Providence, then it is also certainly possible that it is Providence, and at least when in doubt, we admit it.

“The same problem arises with respect to every confession to God for a miracle and salvation”
And the same problem arises with those who pray to be saved from trouble. After all, every prayer of David is for good.

To Mr. Aharon Tabori,
I would be happy to share with you an incident that happened with Maggid Meisharim Rabbi Reuven Karlenstein zetz”l
About 30 years ago, the Rabbi needed a kidney transplant and left his family and flew to Boro Park where he waited two years for a kidney transplant and did not get one. (Because of his blood type)
One of the activists suggested moving to a hospital in San Francisco. And the Rabbi raised concerns about his lack of knowledge of the language (from a hospital in Boro Park). The activist suggested that he fly with him. The flight took 6 hours and they arrived at 3 am.
At 6 am, police officers knocked on the door of their hotel room and announced that the Rabbi's wife was urgently looking for him. 2 kidneys were found that were suitable for the Rabbi in Boro Park.
The activist was stressed and immediately called Boro Park but delayed the appointment by fifteen minutes. And the kidneys were given to those coming in line.
In despair, the worker returned to the R.A. And the R.A., sensing this, extracted the truth from him. And he immediately began to dance and thank the R.A. The worker asked: What does this do for joy?? And the R.A. replied that he was “thankful to the R.A. for the miracle of not putting a kidney that was not his into his body.” And he returned and called his family to inform them of the great miracle that had happened to him.

It is reasonable to assume that any other person would already be certain that heaven had decreed for him to receive a kidney transplant.
In any case, the R.A. waited another two months and a suitable kidney was found and he lived another 30 years in health.

And the other kidneys?
The worker followed the transplanted ones and it was discovered that they lasted a month and died. Because the kidneys were contaminated from the inside.

Is there any point and reason to thank God for the creation of the world?

The dissenter, allow me to refer you to this response https://forum.otzar.org/viewtopic.php?t=33741&start=120#p365722
This is a response to two stories that were brought up there earlier, which are similar to the story about Rabbi Karlenstein.