1) This can be reconciled on the basis of the Gemara here (end of 9a) which answers that the reason why the "Man" came down in the merit of Moshe Rabeinu was that Moshe was different. Since he requested the Man for the community he was not considered as an individual but instead was considered as "Rabim."

2) There is an alternative text of this Gemara, printed on the side of the page, that states "since Moshe Rabeinu possessed a strong merit, he was equivalent to many."

According to this text we can understand also why the world was sustained in the merit of Rebbi Chanina. He also possessed a strong merit, and therefore plenty was granted to the world in the same way that it would be granted for the merit of the multitudes.

3) According to our text in the Gemara, we can also reconcile the Gemara on 24b. When the Gemara says that Hash-m does not give Parnasah b'Zechus Yachid, this means that if the individual needs the Parnasah for himself, Hash-m does not send plenty for everyone merely because of the needs of the individual. However, Rebbi Chanina ben Dosa anyway did not receive plenty, as the Gemara (end of 24b) tells us, that for him a Kav of carobs was sufficient from Friday to Friday. Since Hash-m was not sending the plenty for him, it could be sent for the rest of the world, and Rebbi Chanina also received what was sufficient for him.

4) Moshe Rabeinu and Rebbi Chanina ben Dosa were not private individuals who lived only for themselves. Their entire lives were devoted to helping others. Therefore, they had a Din of Rabim, and Hash-m sent plenty in their merit in exactly the same way that He sends Parnasah in the merit of the masses.

5) I then saw that your question is asked by Rav Yosef Engel zt'l, in Gilyonei ha'Shas here. He writes that there are a few ways to answer this question, although he does not explain. He does refer us to the Maharsha here.

Presumably, he is referring to the words of the Maharsha in DH Matar. The Maharsha distinguishes in a different way from Rashi between Matar and Parnasah. The Maharsha writes that Matar refers to rain that comes down naturally from Heaven. If an individual is in need of this, it will be granted to him for the needs of his livelihood according to his merit. However, Parnasah means something very different. It refers to miraculous occurences, such as the Man or the well that Bnei Yisrael received in the desert. Since this is a miracle, it only happens for the public, as the Gemara states.

According to this, the question from 24b can now be answered. This answer in fact is given by the Sefer Tehilah l'Yonah here (published in Lakewood in memory of Rabbi Yonah Weinstein zt'l). The blessing that came into the world through the merit of Rebbi Chanina ben Dosa was not similar to the Man and the well. It was a blessing that occured in a natural way, according to the laws of nature, but it came through the merit of Rebbi Chanina.

The Tehilah l'Yonah goes further and writes that according to the above Maharsha, another problem can be solved. The Gevuros Ari (by the author of the Sha'agas Aryeh) on 2b asks an apparent contradiction. The Gemara there states that according to Rebbi Yochanan, "Geshamim" (rain) is identical with Parnasah. How does this fit with the Gemara on 9a, where Rebbi Yochanan himself clearly distinguishes between rain and Parnasah? The Tehilah l'Yonah writes that according to the Maharsha, there indeed are two kinds of Parnasah. The Parnasah referred to on 2b is Parnasah derived by natural means. This is similar to rain which is also natural. In contrast, the Parnasah referred to on 9a is derived miraculously, as the Maharsha writes, and this is not similar to the natural Matar.

In fact, the above answer to the question of the Gevuras Ari is a strong support to the Maharsha. To answer the question of the Gevuros Ari we must say that there is a different kind of Parnasah. The latter assertion was made explicitly by the Maharsha. The Maharsha himself did not mention that his explanation also incidentally resolves the contradiction from 2b, but now we see the depth of the words of the Maharsha -- that with his new interpretation, he resolved two problems with one answer.

Kol Tuv,

Dovid Bloom