I wish to argue that rather than either manga or webcomics being superior, one should consider what the strengths of each medium are.
Webcomics allow for deeper emotions(we're not speaking of emotional impact here, but of quality and variance) due to their slower pace. Webcomic readers tend to feel more immersed, as the slower pace allows the readers to "linger" in the scenes longer. Fight scenes can work in webcomics, too, as it all depends on how you array the panels and how you utilize the format. That said, the said fight scenes would be slower-paved than almost any fight scene in a manga, no question about that.
Manga allows for strong emotional moments(how many times have we cried when we happened upon a particularily emotional scene) and perhaps(emphasis on perhaps, as your mileage will vary) the best action that comics have to offer. This all does come at the cost of it all being over perhaps too quickly, as the manga format tends to have breakneck pacing because of how its panelling works. However, this same flaw allows for manga stories to unfold much faster and allows mangakas to tell epic narratives through their art...
As you folk can see so, this isn't simply a question of listing pros and cons, seeing as even the flaws inherent to each format can be utilized to become a strength. I think that when manga readers hate on webtoons, it's because of their slow pacing. Likewise, Webcomic readers might feel that manga(as a format) is too "shallow" in terms of emotional variance.
I will have to state at the end of my arguments, however, that they're very much coloured by my own perceptions. Regardless, I'd like to hear your thoughts on manga and webcomics.