These two sonnets that you mention are ones where Shakespeare talks about other poets (not by name) and even sees himself as inferior to them.
In Sonnet 80, he is saying quite clearly that he is not as good as the other poet. He is saying that the other poet is so much better that he, Shakespeare, gets discouraged. The only hope, if you can call it that, is that at least if his ship (his love) wrecks, it was in a good cause -- trying to win the subject of the poem.
In Sonnet 82, the speaker is saying that his lover can read other poets' works. And his lover might even like them. But his own poetry is better because his lover is so beautiful that plain words (like the poet's own) are better than fancy ones like the other poets use.
Shakespeare's sonnets are arranged into three four-line quatrains plus a concluding two-line couplet. Each of the three quatrains usually explores a different variation of the main theme; then, the couplet presents a summarizing or concluding statement.
Shakespeare's Sonnet 80 is a very despairing sonnet as in the first quatrain the speaker expresses his discouragement at learning that another poet writes about the lover; in the second quatrain he fears losing the attentions of his lover because his verse/his "saucy bark [is] inferior" to that of the other poet who praises the lover.
Then, in the third quatrain the thought changes, and, using the metaphor of a boat for himself the speaker asks the lover to "hold me up afloat" while the other poet receives favor; for, if he loses the favor of the lover, he will despair: "I am a worthless boat." The final couplet draws the conclusion that if the lover praises the other poet, and ignores the speaker, the lover will become the cause of the speaker's "decay."
In Sonnet 82's first quatrain, the speaker admits to the lover that the lover has no obligation to his poetry and has the right to survey without guilt the words of other poets. In the second quatrain, the speaker admits that the lovers beauty is and skills are beyond his ability to describe them, so the lover
art enforce'd to seek anew/Some fresher stamp [representative] of the time-bettering days
Then, in the third quatrain, the poet counters these admissions that even though the lover seek other expressions, the simple, straightforward praise of the poet makes him "Truly fair." Finally, the couplet expresses the idea that the more artistic endeavors of others are wasted on one who does not need embellishment, for "in thee it [embellishment] is abus'd"
This sonnet (82) indicates that the speaker is regaining his confidence in his ability to more honestly praise the lover, even if he is not as artistic as the other poet.