Well, in some ways, we can say we are more lucky to be alive in this day. Our Writings speak of how the Prophets have all yearned to witness this Day.
So, we should be grateful.
On the other hand, God is merciful to each soul. The other souls who have past are judged according to the standards of their time. They were able to find joy, despite hardships which perhaps today we could not bear. And God compensates those who face hardships.
But essentially, many of these questions are in fact mysteries. The Universal House of Justice itself states:
"The world is clearly beset by ills and is groaning under the burden Of appalling suffering. The trials of the innocent are indeed heartrending and constitute a mystery that the mind of man cannot fathom. Even the Prophets of God Themselves have borne Their share of grievous afflictions in every age. Yet in spite of the evidence of all this suffering, God's Manifestations, Whose lives and wisdom show Them to have been far above human beings in understanding, unitedly bear testimony to the justice, love and mercy of God."
(Messages from the Universal House of Justice 1963-86, p. 661
All creatures are going an eternal process of growth. Each has chances to develop. Although our minds can't fathom it because our sight is limited, God's infiniteness can grasp it. As far as your 3rd question about why we weren't all brought to a higher understanding immediately (or for your 2nd question, why we don't have a greater knowledge now and possibly for your first question if you were hinting at what we might think as the cruelty for someone born into poverty, etc.), 'Abdu'l-Bahá says in the chapter on reincarnation in Some Answered Questions on the need for perpetually growing development:
The idea that existence is restricted to this perishable world, and the denial of the existence of divine worlds, originally proceeded from the imaginations of certain believers in reincarnation; but the divine worlds are infinite. If the divine worlds culminated in this material world, creation would be futile: nay, existence would be pure child's play. The result of these endless beings, which is the noble existence of man, would come and go for a few days in this perishable dwelling, and after receiving punishments and rewards, at last all would become perfect. The divine creation and the infinite existing beings would be perfected and completed, and then the Divinity of the Lord, and the names and qualities of God, on behalf of these spiritual beings, would, as regards their effect, result in laziness and inaction! "Glory to thy Lord, the Lord Who is sanctified from all their descriptions." [Cf. Qur'án 37:180.]
(Some Answered Questions, Chapter 81
As far as your concern for unfortunates, again from Some Answered Questions, 'Abdu'l-Bahá replies here to a question:
Question.--What is the condition of children who die before attaining the age of discretion or before the appointed time of birth?
Answer.--These infants are under the shadow of the favor of God; and as they have not committed any sin and are not soiled with the impurities of the world of nature, they are the centers of the manifestation of bounty, and the Eye of Compassion will be turned upon them.
(Some Answered Questions, Chapter [urlhttp://www.bahai-library.com/writings/abdulbaha/saq/66.html=]66[/url])