I think that you should give HoN a chance. I suspect that a lot of the talk about the difficultly of the HoN quests is coming from people who tried to shoehorn existing decks into these scenarios. I firmly believe that you can make effective decks for these scenarios with a more limited card pool (especially if you include Beregond as one of your heroes). Sure, if you don't like tactics you're going to be hard-pressed to field a deck that beats the HoN scenarios with any sort of consistency, but I do not think that you need every LotR card ever printed to make a workable deck.
Solo is a different matter, but assuming you are playing with two players, and the other deck includes Spirit/Lore for cancel/healing, you can make a very effective tactics/leadership deck that will serve as your questing and combat deck for the HoN scenarios.
This deck is off the top of my head, but it only requires 1 core set, 3 chapter packs (2 of which you may already have) and HoN:
Errand Rider (HoN) x3
Gondorian Spearman x3
Defender of Rammas (HoN) x3
Vassal of the Windlord (The Dead Marshes AP) x3
Winged Guardian (The Hunt For Gollum AP) x3
Veteran Axehand x3
Beorning Beekeeper (Conflict at the Carrock AP) x2
Citadel Plate x2
Citadel Spear (HoN) x2
Dwarven Axe x2
Horn of Gondor x1
Steward of Gondor x2
Song of Battle (The Dead Marshes AP) x1
Dunedain Mark (The Hunt for Gollum AP) x2
Dunedain Warning (Conflict at the Carrock AP) x2
Swift Strike x1
Sneak Attack x2
Thicket of Spears x1
Behind Strong Walls (HoN) x3
Campfire Tales (The Hunt for Gollum AP) x3
I'm not claiming that this deck is automatic against the HoN scenarios, but assuming you play it with a support deck that can cancel some treacheries, quest during the few "normal" stages, and heal Gimli and Gloin when needed, this can be a very effective deck. I think it's a myth that you have to have all of the cards to make effective decks; certainly, it makes it easier, but there are some very good cards in the core set.
Ultimately, we all have our own preferences of the level of difficulty that we prefer. Personally, I really enjoy the challenge of the new scenarios, particularly the way that Battle and Siege quests have forced me to reexamine tactics cards that I previously may have dismissed. I encourage you to keep an open mind, and consider that even without buying other AP's or Expansions, Heirs of Numenor is something that you might enjoy.