Best house rules and variants to make D&D less heroic

[King of Nowhere]

D

The reason why making boost spells based on concentration is not a nerf at all is that people will just manage to have the source of the boost spells not be on the warfield.
Ex: they pay someone to cast a bunch of boost spells and benefit all from the boost spell by turning into parasites or the boost wizard of the team stay home until he is called for wizarding out of combat.
this is why hitting the boosted person being the solution against the boost spell works better.
(special exception: missing someone with spells that makes it more easy to miss can dispel one of those spells so that someone making itself near unhittable with spells can still be defeated by attacking)

that requires preparation and hiring npcs. can be worked around, and if the players put that much effort, they should be rewarded

[Reversefigure4]

Remove massive damage rule and replace with this: All damage have a DC = damage.

This is not a bad idea. Even if you lower the DC to make it actually doable (so that crits don't auto-kill), remember that every Natural 1 on a Fortitude save is death. Statistically, 20 Commoners with daggers brings death to a PC.

It's worth keeping in mind that DnD doesn't have a lot of good mechanics for avoiding fights (like a social combat system), so you'll need to be pretty flexible, because the grittier you go, the more fighting becomes a last desperate resort rather than a go-to strategy.