This is an interesting question, and I'm glad that you you make the distinction between Shakespeare as the author conveying homoerotic desires through the sonnets and questioning whether the speaker of the sonnet expresses those same desires. I would point out that we can't determine whether these desires are Shakespeare's because he could certainly have employed an alternate persona as the voice of any sonnet, and those expressions do not necessarily reflect the passions of the author.
Personally, I think that to read homoerotic passions into this sonnet is to judge the standards of a British society which existed over four hundred years ago by modern American standards of expected behavior. In our modern American society, we typically expect women to form close friendships with other women and don't generally think twice if those women express an appreciation of the other's beauty. Women may joke that a woman is so beautiful that she commands the attention of all men and women in the room. Yet we don't typically apply these same characteristics to male friendships. I don't think this necessarily reflects the expectations of male friendships in Britain four centuries ago.
The sonnet begins with the speaker calling the "fair youth" of this poem the "master-mistress of [his] passion." Yet he also goes on to say that this man "steals men's eyes" and amazes "women's souls." This young man seems to be an unbelievably appealing person, but I don't think that just because the speaker is able to appreciate another man's charisma, it automatically means that he's expressing some homoerotic desires. Instead, I would argue that this is the voice of a male who appreciates the beauty and sexuality of another man. I believe Sonnet 20 demonstrates that the speaker is content to allow his friend to enjoy the women for which he "wert … first created" and rests in his belief that the love the two friends share is more significant than the sexual attraction his friend shares with women.