I kinda had that thought before, too. I don´t quite believe the exact numbers of Webcomics, but I think they have a very large readership nontheless.
Once my comic started gaining subs over there, a few hundred went over and subbed on Webtoon as well (knowing how lazy readers are that´s not too bad a number for a few thousand subs haha) (for example: I get 300 - 400 views per update on tapas, but only around 30 to 40 likes; same on Webtoon, or even a worse ratio)
I am also in a Webtoon reader Discord of very active readers, and they all know about Webcomics/ know others who read over there, too.
Interaction usually doesn´t match your Readership at all. I´ve come to this sorta rule of thumb: 5-10% fo your readers will interact as far as commenting and liking regulary, At most 1% will actually buy things support you
(never unerestimate how lazy readers are haha)
No matter the actual numbers, Webcomics works as another exposure to gain more readers on my main platforms, and maybe some dedicated fans in the future. It´s serving its purpose ;D