Ent starter

[Linarfin]

Me and my friends play with starter decks (with cards added from boosters but basic themes of starter decks are retained) and we would like to keep them as balanced as possible. But I have a problem with the starter deck with ents. They seem to be too powerful. They're strong and don't seem to have any weakness. Any advice regarding to this? I'm quite a beginner when it comes to TT block.

[Legion]

The Ents are possibly the strongest Starter in TTT block.  Not only do they contain strength 10 companions (and 1 strength 12) with Ent-moot, but they boast the most deadly swarming shadow in the block.  They'll rip right through those Isengard orcs from Faramir.  Southrons can lay down some hurt if they flood the pool, but to be honest they often won't after they've played everyone, so I'd say Legolas is out.  Dunland has no real answer to a Host of Fangorn with Ent Moot.  They need pumps and so can only win 6 skirmishes in the game.  Plus they hate Merry and Pippin running away.

Theoden actually can just about hold his own.  The fellowship is garbage and will seriously struggle to double (though hosting 7 companions will give you a chance), but those Uruks do make the trees think twice: an Uruk Rear-Guard at a battleground is often going to cause a fair bit of pain.  Eowyn is possibly your best bet.  The Warg Riders can just about hold their own if you play low volume, high strength (as in at least a strength 12 minion per turn), but a well timed Boomed and Trumpeted means you must be on guard with Wolf Voices.  However, I don't see the shadow breaking through all those companions, some of whom are very strong (Elite Riders), and the orcs hate those bows,. so just leg it!

[Linarfin]

Thanks for your insight. It's not that Ents win every game, they're pretty much unkillable but it's possible to take more risks and outrun them.
The other things that bothers me is Eowyn, Sister-Daughter of Theoden. If one has cards in his hand, she's impossible to kill, thus she seems to be overly strong.

[Legion]

It is true she's hard to kill, but there are drawbacks.  First off, she still dies to archery and she's no good at rescuing Frodo from a swarm.  If it's Uruks, the damage is normally so great you would have to discard 4 cards from hand which is a huge drawback.  The real killer, though, is that if you are discarding cards in the Skirmish phase, chances are they're shadow cards.  You don't want to be doing that, as then there's a good chance your shadow hand next turn is awful, giving your opponent an easy run.  If my opponent discards their hand in Fellowship, and only gets a few cards out in their next Shadow, it's probably because they drew all Free-Peoples cards.  That's an easy double.

So that Eowyn is good if your fellowship is going to try to run (she's rare for a reason!).  If you want a more stable walk to Orthanc, go with Lady of Rohan.