The Japanese publishers definitely know this is a huge issue imo, unlike what this article says. It's hard not to when a Korean app combining webtoons and manga (Piccoma) has dominated the Japanese Play/Apple store's rankings and shown the publishers the potential of the market. It's kind of humiliating honestly. That's why they're trying to get in on the business by spinning up webtoon studios and doing manga -> webtoon conversions. Some are doing OK, most aren't.
Note for anyone interested in entering the market: Korean webtoons currently consist mostly of a duopoly between Kakao and Naver. When a good webtoon is produced, the studio usually has to sign an exclusive contract with one of them, and they both have either launched platforms in all popular foreign languages, or have bought out the biggest ones, so squeezing in is not very easy. On that note, I'm very surprised this article doesn't mention the alternative: Chinese webtoons. They're pretty huge as well. Another fun fact: It's kind of hard to find "webtoons" if that's what you're looking for, because Naver tries to scare anyone who wants to use that word (they also own the "Webtoon" platform, which is larger than any other in existence in the foreign market). You'll see stuff like "Smarttoon", "Mangatoon", "Vericomix", and other made-up terms that really just mean webtoon.