For my very first comic, i did the old school/traditional comic format, but when uploading to webtoons, i did crop/cut panels and put it into the vertical format. It was a lot of effort for something that gave me zero results in the end.
Now for my ongoing comic, i do it right from the start in the vertical format. I just reduce the image size when uploading.
I have seen some webcomics using the traditional format on webtoons, and not only seems harder to read, but feels like too much is happening at the same time without breathing espace. That's why i preffer the vertical, one panel at a time format.