It's difficult to balance the beginning of a game for players in packs where you have overtuned the Mob AI. A lot of times this results in your base, chests, and life getting blown to bits or set on fire before you even get a chance to make your first Iron sword.
I would like to see a mod that uses the number of days that a player has been active to determine the difficulty, AI, and attributes of mobs in their vacinity. Something like... after the 5th day mobs gain 20% more damage. After the 10th day mobs gain 20% more health, and "rare" level mobs can spawn. After the 15th day mobs can spawn with full armor, and mobs of epic and elite rarity can spawn. There are great mods like Infernal Mobs and Epic Siege Mobs that would be really great if they had a gating system like this, to allow the player to get at least a little prepared for the onslaught.
Difficult Life for 1.7.10 and Scaling Health (most modern versions) both gradually increase mob health, damage, and abilities over time and give the player opportunities to gain extra hearts. But they don't lower difficulty in the beginning.
Its more a matter of AI that needs to be scaled. Mob awareness range, ability to see through walls, ability to pillar up or dig to you, etc. The Zombie Awareness dev was kind enough to add this feature for me... but sadly that mod doesn't have certain AI modifications that I needed, like pillaring up to players.