while being from a small company and how a company manages its artists do play their part in whether an artist is "underrated", that doesn't explain why girl groups and female artists are often criticized more than their male counterparts. that's plain old sexism, sometimes up to straight-up misogyny.
most everywhere women are held to different standards than men and often are criticized for the same things men get praised for.
when irene's male fans started burning pictures of her because she said she read a feminist book, the fact that she is from a top company didn't shield her from the misogyny of that reaction.
when i see international fans, particularly western and women fans, actively avoiding female kpop artists, that's a gendered response that has nothing to do with them being from a small company or being poorly promoted.
at any rate, i don't know that i would go so far as to say that girl groups are underrated compared to boy groups outside of international fan circles. i don't live in south korea or japan even, but it seems to me that often times the general public in south korea is more aware of girl groups/their songs than boy groups/their songs. this is somewhat generalized and here i do say that company influence and promotion play a big part, but generally speaking, (from what i know) its been considered a truism in kpop that girl groups do better on digital charts/sales and boy groups do better in physical sales. boy groups focus on building a dedicated fanbase while girl groups focus on appealing to the general public; this affects the way companies promote them. its why companies often only focus on one girl group at a time, so that they don't end up competing against each other for the public's attention.
ultimately, boy groups and girl groups are marketed differently, so they produce different results. that said, due to sexism/misogyny, girl groups will always face certain difficulties that boy groups don't have to face.