If you're a big fan of the DQ series, which "Hero" is meant to represent, it would seem "off" that you care most about 2 of 11(+?) main characters in the series? To be devil's advocate-y here.
If you predominantly cared only for the DQ games with female protagonist variety, then the lack of that being represented is understandable.
Although nothing much can be said that would be of real consolation, the cultural / majority fan preference is likely what's happened here. Dragon Quest is apparently a major fan favourite in Japan compared to the West, and marketing wise they chose to make the flagship representation be DQ XI; and I've heard a lot about "Eldrick" from III, what are the other two versions popularity factor? Gender/identity are less at the front of social and cultural thought/progression in many countries still, and Japan is an oft described as being "behind", it shouldn't be a free pass or anything but is probably the factor here.
If you're not particularly a fan of DQ games but have a misandrist policy on what you play; that's a shame - while aesthetics is important to the characters I play, a lot of my continually played characters are those foremost that I enjoy the gameplay of, and usually come to love the rest of them incidentally (Marth, ZSS in a nutshell - and my other beautiful brothers, sisters and children). If you end up playing the character and like how they play, I'd hope their physical appearance or identity would be of reduced priority! (just like you'd tend to/are expected of towards people~).
But like,anyone doing their own thing is fine, I don't think you need to justify yourself to others over this preference too much - countless competitive players (including top level) over the years have made it known they will basically only play female characters or prefer them, so you're in good company.
I've barely played through a dragon quest before and know all too well how virulent slime memes/culture is. Personally was most excited to have a "Toriyama" designed character in Smash, haha. "I GET TO PLAY GOHAN / PRETEND IM A DIFFERENT COLORED GREAT SAIYAMAN YEEES"
I think having your voices heard on this is valid; it mightn't change now but if the developer's are given more context to help them empathise with those upset, it might make way in the future.