They are not supposed to work like this. They are supposed to be an emergency measure against invaders, some meat (or wood/rock) walls to hold them up until the army reach there.

If they are intended as an emergency measure only:

- why are there (not one) but two technologies available to all 3 military units that increase both their damage and their armour by 2% for each summoned unit up to a maximum benefit of 10% or 5 summoned units in total. This benefit only applies if these summoned units are on the same island as the military units, not to mention there are 4 variations of these summoned units (2 each), that all of them are unlocked via research.

- unless the enemy choose to fight only on my castle's island, they would still typically (not always) not help anyway.

I feel that the limited research available, especially for the ranger and druid, that leave 1 to 2 technology spots open for these marketplace technologies (and... being tattoo in nature as is the wild elves way) are perhaps designed to be part of their tactics for assaults as well as defence.

The wild elves by comparison to the humans I normally play (dark elves tend to cause my game to crash after some time, and the dwarves aren't my thing), feel offensively weaker on their own. But when I unleash the golems and the treants, for the brief time they are trying to leave the island (and on the occasion when they choose to fight), they improve the wild elves significantly and they seem to be able to hold their own during this time.

I have to disagree with you on this point and say that I feel this technology and spell are part of their play style.