This suggest is a little tricky to explain...
I had a bit of fun in renewed by fighting mordor orcs in Ithilien or gundabad orcs in Lone-lands, or even Eriador. And I spotted a lot of difference between legacy and renewed in term of gameplay.
Without talking about the fact NPCs now got useful shield (and not just decorative) and friendly arrows passing through ally NPCs like they were mist or fog (I will come back of it at the end), something's happening with health bar regen.
In elder minecraft versions, the healthbar always regenerated slowly, but you didn't need to permanently eat in combat because the slow regeneration gradually consume your satiety; opposing to new versions where you instantly regenerates in exchange to get starvish all the time when you fight mobs.
Each one of us will have their own opinion about this, and what regen system they prefer (I prefer the old personnally).
But...
The mod gameplay is very different of vanilla gameplay. Because vanilla mobs are not as dangerous as NPCs of the mod, zombies, skeletons and creeper are easier to check than orcs, Men or elves, archers and warg bombardiers (when they'll be ported) or even trolls. In vanilla, arrows shot by skeletons don't pass through zombies and other mobs. In vanilla, they don't have got shield, they don't have necessarly weapons to deal you more damage. And to conclude, I've the feeling orcs have a higher spawnrate than vanilla mobs in overworld at night (but it's maybe just me). And I don't even talk about trolls, poison effect with poisoned daggers and arrows, invasions, and the other things which will be ported in the future.
Yep, the mod offers a harder difficulty experience than vanilla and when you are permanently harassed at night by more dangerous enemies than usual zombies and skeletons, the old healthbar regen system is more adaptated to this gameplay because orcs are very numerous compared vanilla mobs and it's very (to not say extremely) hard to find respite to eat and heal you before return to fight. And because NPCs are more dangerous than vanilla mobs you're likely to always be wounded, which makes the need of respite to eat and heal more common.
To figure it to you, in the field of Cormallen at nightfall, I could even not travel because the swarm of orcs popping everywhere around. I was forced to stay stuck near a boulder and a tree to ensure me a safe place to eat and heal me whenever I'm too injured to continue without dying. Yeah. I was just stucked until dayrise. That sort of thing didn't happen in legacy. And all of them caused by actual regen system which compels me to ridiculously always eat and so prevent me to longly focus on the battle (which is necessary with the very agressive PvE the mod offers).
So I think we should keep and port the old regen system because healing slowly for eating occasionnally instead always eating is more adaptated to the mod gameplay (in addition to be more realistic, imagine yourself permanently saying "pax!" to eat a burger as you are in a raging battlefield, it's just stupid). Because when you're not hungry, you panick less and stay focus of what happens around you, what is primary when you're permanently surrendered by enemies in wild biomes at night. (It's the case in vanilla too, I don't say the opposite. The overworld is just... less brutal)
I don't have any problem with the shields and arrows passing through mobs. I think it's a good addition and I'll get used to it. It's just the regen system which is not compatible with the hard and agressive gameplay of the mod, undoubtedly more agressive than vanilla. Otherwise, it's the spawnrate of NPCs which needs to be reviewed.
And to finish, I come back of the arrows passing through other NPCs. I noticed they passed through neutral NPCs too. I think it's more obvious neutral NPCs would be hit by neutral arrows as much as enemy NPCs.
But I especially need your opinion about all of this. Maybe you survival experience in renewed (if you did it) have been different of mine.