My issue with houserules, and especially homebrew systems, is that most people aren't game designers, and each house rule adds a small amount of mental load and potential for rules conflicts.
eg. I remember HEMA guy telling everybody about his house rules he wanted for a game of 5e he wanted to DM. He never put it together as far as I know, but he wanted hit tables to determine where you were hit, what happened when a part hit 0hp, etc. Basically making every hit nightmare of tables. Spells were added, changed, or removed based on what personally pissed him off. Not in a "I'm removing goodberry because I want a gritty survival game" kind of way, but a "I'm removing hold person because my fighter dumped wisdom and I kept getting fucked over by it whenever even a low level caster entered the scene" kind of way.
I also object to trying to house rule 5e into something it's not. Want a modern game? Play Savage Worlds, or Everyday Heroes, or Spycraft, or CoC, or fucking anything other than 5e. Want a grimdark meat grinder set in Dark Souls? OSR is right there. Shadow of the Demon Lord is supposedly Dark Souls like. I'm fairly sure there's a Dark Souls RPG.