HP items are not overpowered. In 3s a DG can end in 5-10 seconds already. If you're saying HP items are too good what you're saying is that fights currently last too long, and if that's what you think then you are mistaken.
Outside of 2v2s and 1v1s and HP items aren't a problem. If they reduced the HP of all the DGs via item nerfs they would have to add an HP flag in your base on every map that were intended for 3v3 and up (there effectively is one on Exile already).
You're really just underestimating the variety of favor items which get used already. These ones are used frequently:
- Blood of the Fallen (surprise!)
- Anklet of Speed
- Blade of the Serpent
- Staff of Renewal
- Heaven's Wrath
- Cloak of Night
- Horn of Battle (yes I realize it's inactive atm)
- Ring of Might (same deal as HoB)
Seriously that's not a bad variety at all.
These items get infrequent use:
- Blood Soaked Wand
- Amulet of Teleportation
- Poisoned Dagger
- Symbol of Purity
- Cape of Plentiful Mana
- Totem of Endurance
Does infrequent use mean bad/average players use them but experts don't or just that they have very specific niches? I don't know, but I have seen some of these items used to great effect.
The items that get no usage generally have very straightforward explanations:
- Charm of Life - Shitty version of BotF
- Sam-El's Cloak - Redundant with game mechanics implemented after its creation, ultimately a shitty version of the Anklet of Speed
- Essence of Magic - Incredibly shitty version of BotS
- Mard's Hammer - Not directly comparable in some ways, but still just a shitty version of BotS
- Furious Blade - Characters which benefit from autoattack cap out on attack speed late in the game if they get the items they need anyway. Ultimately a shitty alternative to BotS or Poisoned Dagger
- Totem of War - Shitty version fo Ring of Divine Might
- Pendant of Grace - Not directly comparable but it's generally worse than the HoB
Pretty much all assassin favor items are viable and many of the items which aren't used aren't used because they're worse than other items with identical or similar effects, not BotF. I don't see a problem with favor items that are worse than each other so long as they're also cheaper than the item they're worse than. Just because people who play a lot cap out on favor points doesn't mean that having a price scale is a bad thing.
Favor items by and large are fine and I think the ideal way to increase variety is to add interesting new items rather than nerf the most popular ones.
If you put BotF on the chopping block I guarantee Staff of Renewal, Anklets of Speed, and Cloak of Night will be next, and for me that would dramatically reduce this game's fun level.