I am of two minds on this.
First, I voted that it should say "Company". More precisely, every company within the target formation. Not every company within 18".
But, I also think that it could be interpreted as the formation just takes the increased strength hits instead of passing out the increased strength hits to every company in the formation.
I feel it is more reasonable to have the entire formation take the increased strength rather than every company take the increased strength. Its just too powerful any other way, IMO.
If it were my job to tweak this spell, I would do one of two things:
If a 6 is rolled, every company in the formation instead takes D6+3 Strength 5 hits (Ents instead suffer D6+3 Strength 9 hits)
If a 6 is rolled, the formation instead takes D6+3 Strength 7 hits (Ents instead suffer D6+3 Strength 9 hits)
The first option is still more powerful, but its a lot better than every company in the formation taking 4-10 str 7 hits.
I will aslo say that RAW does not support the assertion that every formation within 18" is affected. This is because of the order of operations in which you must cast the spell. Reading the spell description on page 74:
1st) You must first choose one formation within 18" of the caster.
2nd) you must roll a D6 and consult the results table to find the results.
This is why I beleive that every formation within 18" of the caster cannot be affected by the spell, as the spell clearly states that it has one target. The instructions of the spell make no sense interpreting it otherwise.
Hence why I believe it was just a mistake on the writers part that it should be "every company within the formation" and not "every formation".