It's kinda weird to me. A real lot of isekais state that their fantasy worlds are just like from fantasy games, usually MMO. So why is it that there's always only one guild, the adventurers' guild, that governs over all the adventure-like things? This is not how MMOs work. Just look at SAO. People there gathered into groups and created their own guilds, and I mean like normal guilds, not taverns in which you can take an everlasting (obviously, every town requires from people to register at the guild) and take some fucking sheets from a wooden board.
Edit: I forgot about the bad as fuck ranking system. F to A, F to S, E to A... whatever. Letter ranking based on how many flowers you picked for merchants and how many slimes you defeated definitely could take some changes. There's that one manga where an adventurer gets turned into a zombie, later evolving into a ghoul. He's a low rank, but he has... THE EXPERIENCE. His rank is low, yet he's helped many people way stronger than him. This is what rankings should consider the most, not the number of monsters you slaid.