Sackville's youthful poetry strikes me as being very somber and dark. Even though you mention that Queen Elizabeth described Sackville's conversation in his youth as being “witty and delightful,” I still have a hard time seeing him as the author of Shakespeare’s sparkling comedies based on his extant poetry. Can you expand on your thinking on this topic?
The dark and gloomy style found in Sackville’s earliest poetic efforts, and particularly in Induction, should really be viewed as an early Elizabethan period style, similar to that found in much other poetry of the time including other Mirror for Magistrates poems. No one was writing scintillating Shakespearean comedies yet, and the recent poetic models Sackville had before him were largely somber ones.
What I find more interesting than the dark tone of Sackville’s early poetic works is the evidence of his rich poetic imagination. His two Mirror poems overflow with stories and images of mythical figures, goddesses, princes, ordinary people, and figures from history. They reveal that Sackville was acutely sensitive to human suffering, and that he used poetry to transform his own suffering into art. While the Induction is a bleak poem, it is imbued with a curious sweetness. Sackville and the Goddess of Sorrow hold hands while they walk through a howling desert, and clasp hands on a ferry to hell.
Sackville’s Induction has been called “a bold and gloomy landscape, on which the sun never shines,” but it does not follow that Sackville was himself a gloomy person (although he does appear to have been in a very sad frame of mind when he wrote his Mirror poems, as discussed in Thomas Sackville and the Shakespearean Glass Slipper). From all evidence his nature was balanced between light and dark elements, as was Shakespeare’s. Although his early poetic works are closer in spirit to the medieval atmosphere of Sackville’s youth than to the Renaissance atmosphere that underlies Shakespeare’s works, they are also the sorts of works that one can easily imagine Shakespeare writing if he were a young poet finding his wings in the early 1560s.
If the only three Shakespeare works to have survived were Titus Andronicus, Henry VI Part Three, and A Lover’s Complaint, I think many people would agree that Sackville is a very plausible author of these works, and that they represent a natural continuation of the themes and rhetorical strategies he employed in his youthful works. I think many people would also agree that, based on these three works alone, no one would suspect their author of also being capable of writing the delightful comedies Twelfth Night, As You Like It, and Much Ado About Nothing.
As a final consideration, Sacvyle’s Olde Age gives us a small glimpse into Sackville’s evolving poetic style, circa 1574. Despite being an extended meditation on what it means to grow old, leave youth behind, and face death, Sacvyle’s Olde Age is philosophical rather than gloomy, and rich in Shakespearean language, imagery, and themes. Modern scholars tend to portray Sackville as a serious and solemn man, but he describes his youth as one devoted to “pleasures,” “pastime and play,” “delights,” and “disport and mirth.” Far from being an ascetic, he enjoyed composing lusty ditties and gazing on the beauties of the Elizabethan court.