Shunzei here is referring to how the Japanese word for ‘waves’ (nami) is transformed to the word for ‘tears’ (namida) with the addition of voiced ta (da).
The commentators speculate here that Shunzei’s basis for this judgement is a personal preference for the Right’s more negative outlook, as opposed to the positive one of the Left.
The suggestion here is that the poem conveys too much expectation that event will work out as the poet wishes, and so lacks the nervousness which a proper lover should display.
蓬莱山 a mystical land in Chinese mythology, said to be home to the Eight Immortals. Qin Shihuang sought it in his later years, in search of the elixir of immortality.
This poetry competition took place in 1049, on the ninth day of the Eleventh Month. It was a fifteen round contest held at the court of the Emperor Go-Reizei. Sagami’s poem, on the topic of Love, was presented in Round 14.
In their comment on the Left’s poem, the Right use the expression asahanaretaru . There are no other examples of this term in the classical Japanese canon, and so we are reliant on Shunzei’s comment about its meaning. From what he says, however, it appears that it was relatively obscure, even to him.