When playing the original game, I tend to do Level 6 after level eight. I think the problem isn't as much that Level 6 is too hard, but in contrast to it, levels 7, and 8, are too easy. The main difficulty for Level 8 was in locating it, but once this was well-known, it wasn't a problematic level. part of what makes L6 so bloody difficult is the abundance of LikeLike enemies, that eat your protection against the Wizrobes.
Playing L6 comes down to tactics, using the wand, and the bow, to attack LikeLike enemies at range. Running out of bombs in some levels can also be a game-killer. I don;t recall if it was in Level 5, or Level 6, where there are some Gibdos, behind a one-way shutter, and to make progress, you need bombs; but there is one room that can require a 'continue' to escape, if you run out.
I tend to find that the Darknut rooms in some of the levels are far more challenging than L6, particularly those that are mandatory to open a hidden staircase.
Overall, L6 is more difficult than the levels before it, due to enemy combinations. L7 is a pain, due to needing to find passages, and isn't really any harder, or easier, than L6; but L8, by the time you get to is, is about as difficult as L1. That, IMHO, is what makes L6 seem much harder than it should be.