Yes but at this point it is getting a bit ridiculous. he author could drag it out a little more. I know this manga is about a harem but at some point, he should have to work for it and not just be handed girls. I mean a queen just handing over her daughter to a low ranked healer just because he cured her sight. I mean would she have done that to anyone who cured her sight. Come on try to add a little thought to the plot.
I mean it isn't just him being the only healer in the kingdom in the last 50 years to be able to cast Extra Heal, it is also that she knows how fast he learned it since she was the one who donated the book to be gifted to the clinic. So he isn't just a low ranked adventurer with healing magic, he is a low ranked adventurer with healing magic who can learn an incredibly complex spell that would normally take decades to learn in what was it a month?
As boring a plot point it might be, it isn't exactly unrealistic. Throw in the fact that they could mobilize the elves purely because of his connections and you get a result where his political value is off the charts. Oh and as an additional advantage his 'family' consists of the Demon Lord Slaying Hero, the greatest Elven Warrior, and an Assassin who can fight on par with the other two. Her daughter might very well be safer in his household than in the Palace itself.
So the boring issue is the instant falling for the one who heals you trope more so than the Queen being willing to promote trying to tie what may be the most powerful family in the country to the throne. May have been more interesting is the Queen was handing over her daughter in an attempt at political maneuvering, but that would also be rather out of character for this manga. It is what it is.