To be honest, I think most readers don't care all that much as long as the comic is readable.
As creators we tend to overthink these things while I think the casual readers don't care as much for the format of the comic, like they wouldn't avoid a comic just because it's in the traditional format, the evidence being that there are so many popular comics that are in traditional format, even ones that update 1 page per week that are super popular. They don't update all that often and it's less content that a vertical format comic yet they're still popular due to other factors.
I like the vertical format so much because it helps me so much as a creator, I can make the conversations flow better, I can pace the scene better, the episode never feels packed bc of the spacing, I can add panels whenever I want if I change my mind about something. I read on my mobile too so reading a vertical format is easier but as long as a traditional format comic is legible and easy to read then I don't mind.
I think a creator should just go for which ever format suits their workflow and comic, reader are used to webcomics being in either format, they'll sub if they like your art and story.