: to esteem too highly.

What does it mean to underestimate someone?

: to estimate (something) as being less than the actual size, quantity, or number. : to think of (someone or something) as being lower in ability, influence, or value than that person or thing actually is. See the full definition for underestimate in the English Language Learners Dictionary.

What does so overrated mean?

If something or someone is overrated, that person or thing is considered to be better or more important than they really are: In my opinion, she's a hugely overrated singer.