Agil combining with Ekimu does look different than the Toa combining with their creatures does. I think that the Toa, Okotans, and by extension Ekimu are beings of one of the six primary elements first and of light second, so for a creature of light to create a "Toa of Light" even temporarily it has to provide a much larger power-up than any of the other creatures would if they were to temporarily combine with any Okotan of their element. Best I can guess is that, between the power-up required and how much energy Ekimu expended just to counter the (also significantly powered-up) shadow powers of Umarak the destroyer, Agil was basically expended to give the Toa their moment to stop Makuta. RIP Agil, you died (were expended) for a more noble purpose than JTO made it seem.
Then again, it's been a while since I've seen the end of JTO, so I could have some things wrong on the details.