The poet in "Life" says that sages describe life as dark and gloomy. Does she agree with them?

The opening lines of "Life" read:

Life, believe, is not a dreamSo dark as sages say

From these lines, and specifically from the word "not," it would appear that the poet certainly does not agree with the sages who say that life is "So dark." In the next few lines, Brontë uses nature as a metaphor to argue that the bad moments in life often give way to, or are necessary for, the good things in life. For example, she says that "a little morning rain" will often indicate " a pleasant day" to follow, and that "clouds of gloom" are "transient" and so will pass. She also asks why we should "lament" the rain when the rain is necessary for "the roses (to) bloom."
In the middle of the poem, Brontë encourages the reader to enjoy "Life's sunny hours" while they last. This attitude is known as carpe diem, meaning to seize the day. She acknowledges that "Death at times steps in" to our lives, and that sometimes "sorrow seems to win," but she also says that "Hope again elastic springs." In other words, no matter how much death and sorrow one might experience, hope will always return, "Unconquered, though she fell."
The final lines of the poem definitively point to the fact that the poet disagrees with the sages who say that life is "So dark." Brontë exclaims in these final lines that we should "fearlessly" bear our trials and tribulations because, "gloriously, victoriously, / Can courage quell despair." Brontë's message is thus that we should always confront the dark times with courage, knowing that light, in the form of hope, will always return.