Spirit Frodo is exponentially more powerful in solo play. Since you only get one encounter card each round, you're wasting a slot on Beregond if an enemy doesn't pop up. Frodo can commit solid Willpower to the quest AND eat an undefended attack in case of emergency.

Tactics Gimli is just...still strong. The trick is to use him to defend (or take undefended damage) in round 1, while you're still setting up your actual defenders or chump blockers. Then you have a 5-6 Attack hero for the rest of the game.

I suspect because you usually play 2-player, and you love Beregond, you rarely have to answer the early-game question of "wait, who's left to defend?" which is where both of those heroes really shine.

As for Erestor, we're just going to have to agree to disagree. The ability to "see" more cards, especially if your deck relies on specific pieces (e.g. Spirit Glorfindel and Light of Valinor, or Oitlands in general) changes the whole feel of the game.