> 95% of this is covered by a warning that says "I won't merge any PR that a) does not pass linting (configured to my liking) and b) introduces extra deps"

Maybe I'm not up to date with the bleeding edge of linters, but I've never seen one that adequately flags

    let out = []
    for(let x of arr){
      if(x > 3){
        out.append(x + 5)
      }
    }

   let out = arr
             .filter(x => x > 3)
             .map(x => x + 3)

Indeed, yours has both more allocations and a bug (+3 instead of +5)