Hotaro actor may be new to acting, but TOEI is NOT new to choosing actors for their most popular series...
I think the factor is not only that,there is too many filler, and to many ideas that hey tried to comprees in final arc, they tried very hard to make the main character cheerful, enthusiastic and optimistic, always smiling like in shounen anime...even though not everything from anime can be adapted to the real world... And I think Toei also failed in this regard, I think ichinose is very cringe and annoying, the acting of the heroine and the writing of the series are also not able to make up for that shortcoming
I think they themselves are also aware of this, that's why there are 3 "cold" characters in this series to balance the cheerfulness of ichinose_(kurogane, legend, daybreak)... You can argue that it's everyone's opinion whether a moment is comedic or cringe-worthy, but it seems that the ratings of this series agree with me.