That means for isekai stories only the flavor text would change. Guilds would turn into legions, if any. Slaves would have a few more rights. People would be a lot less dirty and sick. That's about all an isekai writer would change to make their story "unique" while still using the "How to isekai: writing a story with the minimal effort 101"-template.
I'd love to see a colonial isekai (minus the slavery thing) or a victorian one minus steam punk and/or vampires.
Why isekai = lazy writing?
And anyone could do anything, but pulling it off is the challenge. They might treat others better, but at the same time, there might not be the sanctity of life present. Which would mean that they would treat an average life less than other things (like honour, family, tradition)
There will be coins but many things would be impossible to be bought without someone to vouch for you or due to the absence of available products.
There might be rules and laws but they would be outrageous by our standards. Quite a lot of early justice systems would side not with the truth but with the side that had more influential backers (not because of the corruption but because if you have renown that made you automatically a better person compared to some unknown peasant in their eyes.)