Bruh i understand you saying that abt isekai manga 100% , but manhuas are on anothet whole lvl coping each other, you can find literally 1k manhuas where soke goddamn immortals get reincarnated as some city guy and get some rich girls attracted to them , as for manga abt isekai at this point its like chinese manhua, the reason why there are so many of them , and having similar plot is because around 50-60% of isekais/fantasy are adapted from novels, and some of them are originals , generally the best ones arw adapted from novels .
Well i generally follow manga from shonen jump and weekly shonen magazine like rental girlfriend, black clover etc.etc. so when they hv a break like this week, i just see the top 6 hourly and daily chapters and out of 10, 5-6 are isekai ,this thing goes on for like ,365 days lol, and that pretty much sums up how many isekai mangas are there and also there many mangas which are left untranslated , so it just sums up how many isekai would be there,i just think this, right now i m not living japan ,and i get these manga fr free, just how much would i have had to spend if i lived in japan and followed isekai altho yen is weaker compared to country's currency, but still it d cost quite a lot