To be: I am. You are. [S]he is. They/we are.
Etre: Je vais. Tu es. Il/Elle est. Nous sommes. Vous etes. Ils sont.
Ser: Yo soy. Tu eres. El[la] es. Nosotros somos.
Estar: Yo somos. Tu estas. El[la] esta. Nosotros estamos. Ellos estan.
I think that pretty well sums it up.
I think the point you are making is grammatical: in pretty much any language, the most common verbs are irregular.
But isn't this poem more about orthography and pronunciation? Some languages are much more regular than english in that regard.
It's the other way around: if a language retains some irregular forms, then only because they're common enough that native speakers can remember them.