In Italian opera, the libretto is a vehicle for the voice, in Wagner, the voice is a vehicle for the libretto.
I'm going to tell myself that you don't speak or read Italian in order to grant you clemency for saying something so silly. Time and again, I listen to familiar pieces with far deeper appreciation when I come to see how the musical setting, especially the vocal line, underlines, accentuates, or embodies some idea in the text. The reason Donizetti, Bellini, and Rossini are considered the three giants is not only because they wrote pretty melodies that show off the voice; it's because they wrote characteristic vocal melodies that took texts of variable merit (and some, especially Romani's libretti for Donizetti and Bellini, had considerable merit) to their expressive extremes.
Donizetti: L'elisir d'amore / Act 1 - "Una parola..chiedi all'aura" - YouTube
This duet from
L'elisir could be listened to as nothing more than a pretty melody. Look a little closer, and you will see that Donizetti is drawing out certain words over multiple notes: for example, when the flighty Adina sings about the breeze that flutters over the grasses and lilies, "senza posa", without resting, the word "posa" is drawn out so that the melody does not come to rest either, but hovers over the cadence for a moment. This is a small effect, some critics might even denigrate it as a "trick" -- I should emphasize that this hardly exhausts Donizetti's expressive techniques, even in this piece, is one tiny example -- but multiply it, and many others, over many such moments of poetry, then add in a singer who is sensitive to the expressive potential of such moments, and you have something powerful.
The simplicity of the orchestration allows the
text to be heard, and bel canto technique emphasizes clarity of vowel because the
text matters! The effect of light and dark shading, of soft and harsh timbre, in other words, those contrasts that Italian voices were trained to allow for, all this was essential to singing the
text. In Italian opera, the vocal line is the primary means of expression -- of what? Of the emotions, dramatic situations, and characterization indicated by the
text. In many cases the music exceeds the text in quality, but that's true for many of Wagner's works as well.
In Italian opera, the voice is a vehicle for the
text; if they figured out how to make that vehicle a Ferrari, and if the driver threw in the occasional doughnut for fun, so much the better.