Let's analyze Core set Lorien Guide almost 9 years later against a full Spirit card pool.
As of Cycle 9, AP 1 (Vengeance of Mordor - Wrath and Ruin), there are 56 allies, and the average across all of them gives these stat values per point of resource cost: 0.57 , 0.33 , 0.34 , and 0.79 .
Lorien Guide's cost of 3 means it needs 3x the above, or 1.75 , 1 , 1 and 2.4 to meet the Spirit ally card pool average. Clearly it falls short in willpower, defense (which likely doesn't matter as you will be questing with this card every round or using it as a desperation chump blocker), and health (barely).
However, this card has a subtle bonus. Adding one progress to an active location is roughly equivalent to adding 1 as long as you have an active location. This brings the equivalent to 2 - which is just above the cost to willpower average for spirit allies.
Another minor downside to needing an active location is this bonus is almost useless on the first turn of play - since the turn sequence does not allow you to have an active location until after you quest. However, the odds of this card being able to be played (much less desired to be played) on turn one are low - unless you mono-sphere Spirit or have some other resource generation on turn one.
The upside of this bonus making it worth more than one , is if you fail a quest - either intentionally or by happenstance - yet still have an active location with one point left before it is explored. Lorien Guide will clear that location, allowing the group to travel to another one and remove its threat from the staging area.
This becomes equivalent of up to 5 , on the next round. Opening up travel a round earlier after a quest fail, means you no longer need to overcome that threat next round to progress - and this benefit applies even if the Lorien Guide is killed off during the quest phase the next round!
Of course there are many other cards in sphere that do similar function of placing progress on a (active) location, but they all have drawbacks (and advantages) compared to Lorien Guide:
The Riddermark's Finest will progress 2 on the active location, but you must exhaust (can't quest with it) and discard it (!) to do so. Strength of Will also places 2, but you must have drawn this card, must discard it, and have a Spirit character non-exhausted - which means you likely didn't get its use during the quest phase. Steed of Imladris is repeatable and also progresses 2, but has recurring usage costs and takes 3 cards to set up: (1) a restricted slot on a hero, (2) the Steed itself, and (3) a discarded card on each use. Woodland Courier with one less cost and one less is not repeatable without "Silvan bouncing" actions, and will only add 1 location progress once on entering play.
Out of sphere, there is the overpowered Asfaloth. But it is out of sphere, and regardless, it can work in conjunction with Lorien Guide.
Lorien Guide still retains a niche after all these years. One card, decently survivable with 2 , and since you are questing each round, the recurring bonus takes no effort or action outside of making sure there is an active location.
I'm not suggesting that Lorien Guide is a "must play" ally. But it is still a good card with a unique bonus useful in some situations and deck builds.
This recurring bonus helps it overcome its initially poor looking 3 cost, 1 ratio, especially if playing progression style.