In, re: four crop rotation, I'm assuming you've read/are talking about Master of Ragnarok? I've read few isekai, but that one seemed overall tolerable. The world is not given to the protagonist on a silver platter, he actually has things go wrong and makes mistakes, and the unwanted harem seems more for laughs than an endorsement of polygamy. It has its problems, but it also has some genuine quality, in my opinion.
I've also read a Western isekai/litrpg/xianxia crossover called The Ten Realms, which has its own issues, but does bring a unique take. The heroes are former US military personnel, and their power stems from their philosophies of freedom and self-improvement more than having guns in an overall low-tech world.
I first encountered it in "Be mine, Hero!" "I refuse!" / Archenemy and Hero. It wasn't an isekai story, and the Demon Lord(ess) introduced four crop rotation as part of a larger plan to revitalize the agricultural sector. After that however, in other generic isekai trash that my brain refuses to remember, I've seen heroes introducing four crop rotation, winning the acclaim of the local village, and... then, nothing. At least in the former, you see the long-term effects through increased prosperity, reduced starvation and famines, etc.
I think seeing a clash of philosophies, ideas and worldviews is far more interesting in an isekai setting than simply having the MC introducing modern tech and watching the consequences unfold. If the world isn't so radically different from ours that the hero doesn't have to adapt and has no need to face the consequences of living as a modern human would, there isn't a need for an isekai premise. Case in point, Knights & Magic, where the MC is a reincarnated isekai'd modern Japanese salaryman, but his past life barely comes up at all.